Daniil Medvedev says it is a "joke" that players do not have longer at changeovers but will not "cry about the heat" after coming through his Tokyo 2020 opener, while Novak Djokovic started at a canter as he looks to add the next step of a Golden Slam.

Representing the Russian Olympic Committee, Medvedev appeared fatigued at times in his 6-4 7-6 (10-8) triumph over Kazakhstan's Alexander Bublik at the Ariake Tennis Park.

The conditions in the Japanese capital were sweltering on Saturday but Novak Djokovic was able to keep his cool in coasting to a 6-2 6-2 win against Hugo Dellien.

MEDVEDEV CALLS FOR MORE TIME

Medvedev, who saved three of four break points and now has a 3-0 head-to-head record over Bublik, was pretty pointed about what he feels should be done about the heat.

"Like they do in Mexico, the matches maybe should start at six (pm) because the heat actually gets much, much lighter. We all try to practise at six," said Olympics debutant Medvedev, who next plays Sumit Nagal.

"The fact that we have only one minute between changeovers is a joke. If you ask, let's say 200 tennis players that are here, I think 195 will tell you that one minute is a joke. It should be 1:30.

"But you have to play, that's the Olympics, you go for the medal. You're not here to cry about the heat. It was really tough for both of us. We talked about this after the match on the court. It was unbelievably hot. But you need to get through it."

Fellow Russian athlete Aslan Karatsev (11) defeated Tommy Paul 6-3 6-2 to set up a meeting with Jeremy Chardy, while Lorenzo Sonego (13), Ugo Humbert (14), Fabio Fognini (15) and Alejandro Davidovich Fokina (16) all progressed.

DJOKOVIC UP AND RUNNING

Since winning bronze in Beijing 13 years ago, Djokovic has not had the best of luck at the Olympics – losing in 2012 and 2016 to Juan Martin del Potro on both occasions.

But with a host of big hitters from the ATP absent – including Roger Federer and Rafael Nadal – Djokovic is the overwhelming favourite in Tokyo.

Only Steffi Graf in 1988 from either the WTA or ATP Tour has ever completed a sweep of all four slams and an Olympic gold in a calendar year, and Djokovic needs Olympic gold and victory at the US Open to match the feat.

He needed just 61 minutes here to beat Dellien of Bolivia.

MURRAY SCORES UPSET DOUBLES WIN

Andy Murray is the two-time defending men's singles champion in Tokyo, but struggles with injuries mean it would take a herculean effort to make it three in a row.

But he is also representing Great Britain in the doubles and together with Joe Salisbury upset French second seeds Pierre-Hugues Herbert and Nicolas Mahut 6-3 6-2 in their first time competing with one another.

Murray is not looking too far ahead, though, saying: "You take one match at a time, you know, so a lot of the players here are really motivated to play for their country. 

"This is such a rare opportunity for all of us and I think we all want to do well. So, yeah, just take it one match at a time."

Top seed Denis Shapovalov's Swiss Open Gstaad campaign came to an abrupt end as Vit Kopriva provided a second-round shock to eliminate the Wimbledon semi-finalist.

The world number 10, who has recently been praised by both Roger Federer and Rafael Nadal, took the first set 6-2 with ease before Kopriva, making his ATP Tour debut this week, emphatically fought back 6-3 6-2 to secure a memorable comeback victory.

Number three seed Casper Ruud battled past Dennis Novak 6-4 7-6 (7-5), while Benoit Paire, who only had two ATP wins in 2021 before the Hamburg European Open last week, was 6-4 to the good before Tallon Griekspoor was forced to retire due to injury.

Ruud, who has already won two ATP events in 2021 and three in his career, will now meet sixth seed Paire in the quarter-final stage.

But eighth seed Feliciano Lopez did not enjoy similar success as the world number 96 Mikael Ymer fought past the Spaniard to win 6-7 (6-8) 7-6 (9-7) 6-4 and set-up a quarter-final clash with Kopriva.

At the Umag Open in Croatia, third seed Filip Krajinovic breezed past Radu Albot to record a 6-4 6-2 win.

Krajinovic's countryman and number two ranked player Dusan Lajovic also went through with a 7-5 6-4 win against Bernabe Zapata Miralles.

Novak Djokovic has been burned by high expectations at the Olympics before, so it was little surprise that he should express only guarded optimism on the eve of the Tokyo Games.

The Serbian, who has won the Australian Open, French Open and Wimbledon already in 2021, is chasing the gold medal that would leave him one step away from the first tennis calendar 'Golden Slam' by a man.

Should he triumph in Japan over the next fortnight, Djokovic will head to the US Open in late August needing to win in New York to complete the full set.

Steffi Graf, who in 1988 won all the slams and gold at the Seoul Olympics, is the only player in tennis history to have completed such a sensational season.

Djokovic said such a feat was becoming a "more and more realistic" target, as he spoke in a Serbia team news conference, but the last time he stepped off the singles court at an Olympic Games, he was in tears, having lost in the first round at Rio to Juan Martin del Potro.

There is no danger of Djokovic running into his Olympic nemesis in Tokyo, with Del Potro, who also beat Djokovic in a bronze-medal match at the London 2012 Olympics, not a part of Argentina's squad as he battles back from four knee operations.

Looking at his own prospects for Tokyo and the rest of the year, Djokovic said: "It is still a long way to go ... I put myself in a very good position. But I will take things very slowly and cautiously.

"It's an approach I need to have because in the past I wasn't probably fully experienced in that approach. And I started to feel there were a lot of distractions around that influenced my performance.

"I know there are a lot of things on the line, a lot of history on the line. I'm privileged to be in this position. I worked very hard to be here, with my team, of course. But let's talk about history if everything goes great."

After his singles loss in Rio, Djokovic and Nenad Zimonjic lost in the second round of doubles to Brazilians Bruno Soares and Marcelo Melo.

A bronze from Beijing 2008 is all Djokovic has to show for his Olympics career to date, but he is a hot favourite for the title in Tokyo, where he will start against Bolivia's world number 139 Hugo Dellien.

The 34-year-old Djokovic said he "would be delighted to ask" Graf how she achieved her 1988 clean sweep.

"When I was thinking about her ultimate achievement ... I did not think it... I don't want to say 'achievable', but [I thought] there was a slim chance that someone could make it again, both male and female," Djokovic said.

"But right now it seems more and more realistic. Of course, it is one of my goals and dreams."

Djokovic has neither Roger Federer nor Rafael Nadal as rivals in Tokyo, with Federer missing after reporting a knee injury setback and Nadal electing to give the event a miss.

The 'Big Three' each have 20 grand slam titles now, following Djokovic's hot streak, and the Serbian admits it is unusual for both superstars to be absent.

"I have not experienced too many big tournaments in the past 15 years without Roger and Rafa playing. So it's a little bit strange," Djokovic said. "I'm used to seeing at least one of them. But still, some of the best players in the world are here.

"The guys who are in the top six, seven in the world, they are the biggest competitors or candidates for winning a medal. But potentially I am meeting with them in the later rounds."

After winning Wimbledon for a sixth time, Djokovic surprised many by claiming he could skip the Olympics, but he was reeled in by the appeal of representing his country, perhaps for the final time in the Games.

"Without the key element of any sports events – the crowds, the fans, that energy – it's different, but it is still the Olympic Games," he said.

"I was in a dilemma for a little bit, but I decided to come, and I'm glad because there are many more things that are beautiful about the Olympic Games. So I will try to focus on those things."

Novak Djokovic has leapt from one bubble into another as he attempts to become the first man in tennis history to win all four grand slams and Olympic gold in the same year.

The only men to have won each of the singles majors across their careers, plus Olympic gold, are Andre Agassi and Rafael Nadal, and now Djokovic aims to move to the brink of winning all five in his remarkable 2021 season.

Fresh from dominating at Wimbledon, and with the Australian and French Open titles already in the bag, Djokovic heads into the Tokyo Games as a red-hot favourite, seeking to set himself up to complete a historic campaign at the US Open.

Naomi Osaka will enter the Games with almost as much expectation behind her too, the reigning US Open and Australian Open champion eyeing glory for hosts Japan.

But tennis has thrown up a host of shock results in its short Olympic history. Here, Stats Perform looks at the sport's place in the Games.

WHO'S IN, WHO'S OUT, AND WHAT DOES ALL THIS MEAN?

Serena Williams, Roger Federer and Rafael Nadal have all opted out of the Olympics.

Williams made her mind up prior to suffering a leg injury at Wimbledon, although she is already a member of the career Golden Slam club.

Federer reached his decision after revealing he also suffered a physical setback at the All England Club, and Nadal elected to take a two-month break after relinquishing his French Open title.

Don't expect to see them again at the Olympics, given Williams and Federer will be pushing 43 by Paris 2024, and Nadal will be 38. Federer won a doubles gold with Stan Wawrinka in 2008, but his singles peak was the silver medal he earned in 2012, Andy Murray crushing Swiss hopes in the final at Wimbledon.

Dominic Thiem, Bianca Andreescu, Nick Kyrgios, Simona Halep, Angelique Kerber, Victoria Azarenka and Denis Shapovalov are among other confirmed absentees, with fitness issues a factor for some, less so for others.

The COVID-19 crisis is a mitigating factor in why so many stars are staying away, and directly responsible in the case of some players, such as Britain's Johanna Konta and Dan Evans, who both tested positive recently.

But tennis was only fully restored to the Olympic programme in 1988, after being dropped post 1924, and if players are seen to be favouring the grand slams over the Games, that is not such a great look for the sport.

At a time when the International Olympic Committee has shown it is willing to shake up the sports on its programme, tennis could perhaps do with a headline-making Tokyo 2020.

Murray, the two-time defending men's champion, will target an improbable hat-trick. A hat-trick for the injury-hit former world number one would be a sensation, and Osaka landing gold in the women's tournament would surely be one of the great moments of the Games.

DJOKOVIC FOLLOWING IN THE FOOTSTEPS OF GRAF

When Steffi Graf beat Gabriela Sabatini in the women's singles final at Seoul, it completed what we know now as the calendar 'Golden Slam'. She had already won the Australian Open, French Open, Wimbledon and the US Open, and the feat of the then 19-year-old West German has yet to be repeated.

Now Djokovic is three-fifths of the way to a similar clean sweep of the majors and the Olympics, with the US Open getting under way on August 30 in New York.

He teetered on not going to Tokyo, and perhaps he is to some extent endangering his chances at Flushing Meadows by spending more time travelling and enduring bubble life, while others rest up.

But Djokovic is a fiercely proud Serbian and could not resist a great chance of winning gold for his country. He landed bronze at the 2008 Games in Beijing but in 2012 he lost to Juan Martin del Potro in the bronze-medal match, and a cruel draw at Rio four years later saw him assigned Del Potro in the first round.

Top seed Djokovic bowed out in two tie-breaks to the powerful Argentinian, describing the outcome as "one of the toughest losses in my career".

There is no danger of a hat-trick of defeats to Del Potro, which may help Djokovic. Del Potro has been battling for two years to get back to fitness, undergoing four rounds of right knee surgery in a bid to get back on tour.

RAISING THE BAR AT THE OLYMPICS

How the Olympic village functions in Tokyo will be distinctly different to at previous Games, given the pandemic restrictions in place that could be a real buzzkill.

But in the past there have been countless cases of athletes becoming inspired by their surroundings and going on to perform above their usual level.

It can be a party village, and it can also be an eyebrow-raising experience as global superstars rub shoulders with competitors who might struggle for recognition in their home towns. More than anything, the shared team experience, fighting for a collective cause, can make a middling athlete believe they can be great.

Monica Puig was a massive tennis outsider in 2016 but the then world number 34 won the women's singles, stunning Angelique Kerber in the final after beating Petra Kvitova and Garbine Muguruza en route. That gave Puerto Rico their first ever Olympic gold medal.

In 1992, a tournament that featured the likes of Pete Sampras, Jim Courier, Stefan Edberg and Boris Becker finished with a staggering final match-up of Marc Rosset versus Jordi Arrese, who in his home city of Barcelona was edged out 8-6 in the fifth set by the Swiss world number 43. Nobody would have predicted that head to head for gold.

Similarly, at Athens 2004, Nicolas Massu beat Mardy Fish in the gold medal match of a tournament that featured Federer, Andy Roddick, Carlos Moya and Tim Henman.

In the 1996 Atlanta Games, Lindsay Davenport, who had just turned 20, took inspiration from being the daughter of an Olympian, with dad Wink having played volleyball for the United States at Mexico City in 1968.

Davenport was beginning to make an impact on the WTA Tour but was only the ninth seed at the Olympics, yet she swept through the rounds before sinking Arantxa Sanchez Vicario 7-6 (10-8) 6-2 in the final.

"It's like one of those things I look back on and I'm like, 'Was that me?'," Davenport told The Tennis Podcast last year.

"It doesn't seem like it was real. I'd made the transition to the pro tour pretty well, but I liked hanging out between eight and 16 in the rankings. I was very insecure, unsure of what could I do. I liked doing well but I wasn't sure I wanted to do too well because it seemed really overwhelming to be one of those top players.

"Here I go at 20 years old to Atlanta for two or three weeks, in a setting that seemed so comfortable. Look at all these athletes, you have all different shapes and sizes, you have players that are really working hard but have so much in common and you get to hang out with them, breakfast, lunch, dinner in the village."

Davenport was a future world number one and three-time grand slam singles champion, but at this point in her career being an American at an Olympics in the United States was just a thrill.

"You're sharing this with your team-mates who are some of my best friends in Mary Joe Fernandez, Monica Seles. It was the best time ever," she said.

"By the time the tournament actually started we were like, 'Yeah, I'll go play my match and then we'll go back to the village and we'll hang out', and everything went so fast in those few weeks.

"And there I was left standing, winning at the end because I was so incredibly happy and excited with everything that was going on. I kind of forgot what was my job.

"When it became a reality of even just making the team in '96, it was so huge also for my family with having a second generation Olympian."

Roberto Bautista Agut crashed out to Arthur Rinderknech in the second round of the Swiss Open Gstaad on Wednesday, while fifth seed Federico Delbonis also failed to progress.

Rinderknech, who is ranked exactly 100th in the world, picked up the biggest win of his career in style as he dispatched of second seed Agut with a comfortable 6-2 6-4 victory

In another upset, world number 155 Hugo Gaston laid down an early marker with a first-set demolition of Delbonis, who lost out to eventual winner Pablo Carreno Busta in the Hamburg European Open semi-finals last week, before he triumphed in three sets, 6-0 6-7 (2-7) 7-6 (7-3).

Fourth seed Cristian Garin cruised past Marc Polmans 6-3 6-0 to wrap the match up in less than an hour and seal his fifth ATP quarter-final of 2021.

Another semi-finalist in Hamburg, Laslo Djere survived a second-set scare to eliminate Zizou Bergs with a 6-2 4-6 6-2 win, which sets up a last-eight tie with Rinderknech.

At the Croatia Open in Umag, fourth seed Richard Gasquet battled past qualifier Alessandro Giannessi to secure a 7-6 (7-4) 6-4 victory.

Top seed Albert Ramos-Vinolas also progressed, winning 7-5 6-4 to eliminate Duje Ajdukovic on his home turf.

Fresh off the back of semi-final appearances at the Hamburg European Open, Federico Delbonis and Laslo Djere coasted through their respective first-round matches on the second day of the Swiss Open Gstaad, which included no upsets at the round-of-32 stage.

Delbonis, who is seeded fifth and lost to eventual winner Pablo Carenno Busta last week in Hamburg, cruised to a 6-3 6-3 victory against Leandro Riedi as the Swiss player struggled to make home advantage count.

Seventh seed and loser of the other semi-final in Germany last week, Djere continued his good form and wasted no time in thrashing Brazilian Thiago Seyboth Wild 6-4 6-3.

The other game on day two saw Dennis Novak dispatch of Kacper Zuk 6-4 6-4 and that straight-sets victory means the Austrian will next face the number three seeded player Casper Ruud, who won the Nordea Open last week to secure his third ATP title and second of 2021.

Alongside Ruud, the three other top four seeds - Denis Shapovalov, Roberto Bautista Agut and Cristian Garin - will now enter the draw, after benefiting from byes in the first round of the competition.

There was a surprise at the Croatia Open in Umag, though. Fifth seed Aljaz Bedene went down 6-1- 6-4 to Marco Cecchinato, who will now challenge fellow qualifier Damir Dzumhur to set up a potential quarter-final clash with Richard Gasquet if the Frenchman makes it through his round-of-16 tie.

Benoit Paire made a strong start as the Swiss Open Gstaad got under way on Monday.

Number six seed Paire was a 6-3 7-6 (7-2) winner in his first-round match against Jozef Kovalik.

The Frenchman was not broken in the match, saving all eight of the break-point opportunities he offered up to Kovalik during a competitive 85-minute contest.

Paire's win follows a quarter-final appearance at the Hamburg European Open last week as the 32-year-old begins to recover from a dreadful first half of 2021.

Prior to his run in Hamburg, Paire had only won two ATP Tour matches this year.

Mikael Ymer had to come from behind before he progressed with a 4-6 6-3 6-3 win over lucky loser Enzo Couacaud.

The top four seeds at the ATP 250 event – led by Wimbledon semi-finalist Denis Shapovalov – get a bye through the first round and are therefore yet to begin their campaigns.

At the Croatia Open Umag, meanwhile, Radu Albot came out on top as he claimed a three-set victory over Holger Rune, with top seed Albert Ramos-Vinolas and defending champion Dusan Lajovic not in action on day one.

Novak Djokovic has confirmed he will enter the Olympic Games in Tokyo, with the world number one just two titles away from a first men's Golden Slam.

Rivals Rafael Nadal and Roger Federer, citing respective scheduling and injury issues, have each withdrawn from Tokyo 2020.

But Djokovic confirmed on Thursday he will travel to Japan in pursuit of a groundbreaking achievement.

Only women's tour legend Steffi Graf has previously won all four majors and the Olympics in the same year, doing so in 1988.

Doubles superstars Bob and Mike Bryan held all five titles at once but collected them across 2012 and 2013, while Andre Agassi and Nadal are the only two men's singles players to achieve the feat across an entire career.

Djokovic has already triumphed at the Australian Open, French Open and Wimbledon in 2021, leaving Tokyo and the US Open still to conquer.

The 20-time grand slam champion – a record he tied at the All England Club on Sunday – has entered the Games three times previously but earned only a single bronze medal. Andy Murray is the two-time defending champion.

At Flushing Meadows, Djokovic is a three-time winner.

The 34-year-old confirmed his Olympics plans in a social media post as he sent a message to a young Japanese fan celebrating his sixth birthday.

"Cannot disappoint my little friend Koujirou," Djokovic wrote. "I booked my flight for Tokyo and will proudly be joining #TeamSerbia for the Olympics."

He had said following his Wimbledon win last week: "My plan was always to go to Olympic Games, but right now I'm a little bit divided."

Djokovic added limitations on his travelling party and potentially being unable to watch fellow athletes had reduced the likelihood of an appearance to "50-50".

But he will now feature, even if former Wimbledon champion Pat Cash believes the calendar Grand Slam – winning the four majors but not the Olympics – has to be the Serbian's priority.

Cash told Stats Perform: "It's the Olympics, okay – maybe he wants to do that, but certainly his goal is now to try and win all four grand slams in the calendar year.

"He has done four in a row, but he hasn't done them in the same year, which is very, very tough to do.

"There is a reason why I think one person has done it in [men's] professional tennis – Rod Laver and it was in 1969, so it's not easy to do.

"But I really do think it's in his sights and that has got to be his priority.

"It's absolutely the absolute peak of our sport to win all four grand slams in one year."

Stefanos Tsitsipas made a winning return to action as he reached the Hamburg European Open quarter-finals with victory over Dominik Koepfer in straight sets.

Having lost a five-set epic against Novak Djokovic in the French Open final, Tsitsipas crashed out in the first round of Wimbledon against Frances Tiafoe.

The Greek welcomed a return to the clay courts in Hamburg, though, as he saw off a battling Koepfer 7-6 (7-2) 6-3 in a productive workout lasting one hour and 44 minutes on Wednesday.

Tsitsipas dropped serve in the first game of the match but immediately struck back and was not broken again in the contest.

He forced plenty of break opportunities – 14 in total – and converted three over the course of the match which proved enough for victory at the ATP 500 event.

Four set points came and went for Tsitsipas as Koepfer served it out at 6-5 to force a tie-break in the opener, but it mattered little when the world number four won four consecutive points to clinch the breaker.

Koepfer led 3-2 in the second set but two consecutive breaks from Tsitsipas ended the contest and ensured he booked a tie against Filip Krajinovic in the last eight.

Sixth seed Krajinovic beat a German opponent to disappoint the home fans for a second straight day, though he needed a deciding set before seeing off veteran Philipp Kohlschreiber 7-5 4-6 6-3.

In the Nordea Open, held in Bastad, fourth seed John Millman was a casualty as he went down in three sets to big-serving qualifier Arthur Rinderknech, who had 12 aces.

There was no such drama for second seed Cristian Garín, though, as he saw off Pedro Martinez 6-3 6-3, dropping serve just once.

Roger Federer's body has been saying no for the past two years, but Pat Cash is hopeful the 39-year-old will return for another run on the ATP Tour.

After suffering a setback to his longstanding knee injury during Wimbledon, the 20-time grand slam champion has this week withdrawn from the Tokyo Olympics.

Despite being without much match practice – playing just four tournaments before Wimbledon after coming back from two knee surgeries - Federer was able to make the quarter-finals at All England Club.

However, he suffered a demoralising loss to Hubert Hurkacz in straight sets in the last eight that promoted a fresh round of speculation over his future in the game.

Cash, who won Wimbledon in 1987, hopes Federer will be back despite his recent injury woe.

He told Stats Perform: "First of all, let's hope that Roger Federer will keep going. 

"I think he can, I think he just needs more matches and probably needs to make sure that he's able to last. 

"But your body starts saying no at some stage and it's been saying that for a couple of years now for him." 

Wimbledon winner Novak Djokovic is now level with Rafael Nadal and Federer on 20 slams.

Cash believes judging the Swiss star purely on grand slam titles is not a fair measure of his brilliance, pointing instead to his astonishing record totals of 58 major quarter-final berths and 46 semis.

"He has been the most consistent player that I think we've ever seen," Cash said. "He may not end up with as many grand slams but his consistency is just outrageous.

"All the other players have lost early in grand slams, the Djokovics, the [Andy] Murrays, then the Nadals had lost early in grand slams, Roger just doesn't do it.

"Of all the titles that he's won, I think for me, his most impressive record is how many semi-finals or quarter-finals in grand slams in a row that he got to. It was something ridiculous for 10 or 11 years.

"He never failed at any grand slams and that is just absolutely mind blowing."

However long he tries to play on, Cash insists nothing can sour the memories of an extraordinary career from Federer.

Cash added: "Obviously, he raised the bar as far as the standard of tennis has gone. 

"The other players really had to catch up. Novak admitted it, he said, 'Without Roger there, leading the way, I wouldn't have been as good a player as I could have been'. 

"That's the gold standard of Roger Federer over his career and I'm not sure anybody will be as consistent as him in tennis history. 

"He's just phenomenal the way he plays, and we all of course enjoy the style, his movement. And he's a class act off the court as well."

Federer's status for the US Open, which begins on August 30, is unclear, with Djokovic looking to take the outright lead for major titles and achieve a historic calendar year Grand Slam.

Novak Djokovic will never have a better opportunity to achieve a historic calendar Grand Slam, which former Wimbledon champion Pat Cash says he should prioritise at all costs.

The Serbian won a sixth Wimbledon crown on Sunday, defeating Matteo Berrettini in four sets to achieve a final victory that moved him on to 20 grand slam titles.

With Australian Open and French Open successes also already achieved, glory at the US Open would see Djokovic become only the second men's player in Open Era history to win all four majors in the same year.

Cash thinks the stars have aligned for Djokovic, with issues for his main rivals leaving the 34-year-old primed to achieve the famous feat in 2021.

"The impossible dream really is there," Cash said to Stats Perform.

"For Novak this year it is a great opportunity for him to grab a bunch of grand slams and grab all the titles. 

"Certainly Wimbledon – without disrespecting the other players – was one of the weaker men's side draws that I've seen in many, many years. 

"And that's because we've got two of the big stars coming back from injuries – Andy Murray and Roger Federer – who played well but weren't at the peak of their career.

"The younger players are coming through but they're not quite there yet and Novak is just sitting on top of that mountain as the King of the Castle.

"His performance was exceptional at Wimbledon, there's no doubts about it. 

"The slightly younger players are coming through – Berrettini obviously in the final really pushed him to just about the limit.

"Stefanos Tsitsipas in the French Open final up two sets to love. So, these guys are close, very close, and it won't be long before they catch up with Novak and the others. 

"Obviously Rafa [Nadal] was out of this Wimbledon as well – I don't really think he's a serious threat on the grass anymore but he's still a great competitor. 

"So these guys are catching up, Rafa is still there, maybe Murray will come back and Federer will come back and be in better shape in the next year – but this is the year that Novak can really grab." 

Djokovic admitted this week he is still "50/50" over whether he will take part in the upcoming Tokyo Olympics due to coronavirus countermeasures in the Japanese capital. 

Federer withdrew from the tournament on Tuesday and Cash insists Tokyo will not be the priority over glory in New York for Djokovic.

Cash added: "It's the Olympics, okay – maybe he wants to do that, but certainly his goal is now to try and win all four grand slams in the calendar year.

"He has done four in a row, but he hasn't done them in the same year, which is very, very tough to do. 

"There is a reason why I think one person has done it in [men's] professional tennis – Rod Laver and it was in 1969, so it's not easy to do. 

"But I really do think it's in his sights and that has got to be his priority. 

"It's absolutely the absolute peak of our sport to win all four grand slams in one year." 

With Djokovic now level with Federer and Nadal on 20 majors, Cash would not be surprised to see him build a big lead.

He added: "Look, it's very hard to say. We have all been proven wrong by the numbers. 

"Though most of us thought that Rafa and Novak would get pretty close to Federer, we didn't really think they'd get there and beyond. 

"I think Novak is likely to win another couple, but you know, it takes us one little injury [to derail him] so it is very hard to say.

"John McEnroe said 25 or so [for Djokovic] and that could be well within his reach at the moment. 

"He's improving and that's frightening to think. He's won 19 grand slams before Wimbledon, and all of a sudden we've seen this guy come to the net, volley, add another string to his bow to become a better player. 

"Yeah, age 34 and he is improving – that's pretty frightening." 

Jan-Lennard Struff suffered a disappointing defeat on home soil to Laslo Djere at the Hamburg European Open on Tuesday.

Djere triumphed 6-4 7-5 against the seventh seed to book a last-16 tie against qualifier Thiago Seyboth Wild at the ATP 500 event.

It was a day of missed chances for world number 47 Struff, who took just one of eight break-point opportunities and hit five double faults as he went down in one hour and 50 minutes.

There was no such disappointment for Filip Krajinovic, though the sixth seed had to work hard before seeing off home wild card hope Daniel Altmaier 6-3 6-7 (3-7) 6-1.

Krajinovic will face another German next in the form of Philipp Kohlschreiber.

The number one seed Stefanos Tsitsipas is yet to start his campaign in Hamburg.

In the Nordea Open, held in Bastad, there was a first-round defeat for teenage talent and sixth seed Lorenzo Musetti, who went down in three sets to Swiss qualifier Henri Laaksonen.

Roger Federer has withdrawn from the Tokyo Olympics because of a setback to his knee suffered during the grass-court season.

Olympic gold in singles is one of the few honours missing from Federer's glittering resume, the 20-time grand slam champion having won silver in 2012, losing the gold medal match to Andy Murray less than a month after beating the Briton in the Wimbledon final.

While Murray will be in Tokyo to attempt to defend his title again having successfully retained it in 2016, Federer – a doubles gold medallist in 2008 – has elected not to make the trip to Japan.

"During the grass-court season, I unfortunately suffered a setback with my knee, and have accepted that I must withdraw from the Tokyo Olympic Games," Federer wrote in a statement on Twitter.

"I am greatly disappointed, as it has been an honour and highlight of my career each time I have represented Switzerland.

"I have already begun rehabilitation in the hopes of returning to the tour later this summer. I wish the entire Swiss team best of luck and I will be rooting hard from afar. As always, Hopp Schwiz!"

Federer missed most of the 2020 season due to persistent right knee problems that led him to undergo two surgeries.

The length of his recovery forced Federer to miss this year's Australian Open but he made his return to the tour in time for the French Open, reaching the fourth round before withdrawing to focus on the grass-court season.

Yet he was stunned by Felix Auger-Aliassime in the second round in Halle and was often unconvincing in progressing to the quarter-finals at Wimbledon, where his quest for a ninth title was ended by Hubert Hurkacz, the Pole becoming the first player to win a set 6-0 against Federer at the All England Club.

The 39-year-old's withdrawal makes him the latest tennis big name to pull out of the Tokyo Games. On the men's side, Rafael Nadal and Dominic Thiem decided against competing, while Serena Williams confirmed before her first-round retirement at Wimbledon that she had no plans to play at the Olympics.

World number one Novak Djokovic has said he is "50-50" on going for his first Olympic title. Having won all three majors so far this year, Djokovic is in prime position to become the first man to do the 'Golden Slam' in the same season. Steffi Graf achieved the feat in 1988, with a sweep of the majors followed by her victory at the Seoul Olympics.

Benoit Paire was gifted a place in the second round at the Hamburg European Open by Ricardas Berankis' foot injury, but fellow countryman Richard Gasquet could not get past Marco Cecchinato in his first-round clash in Sweden.

Lithuania's Berankis forced Paire to a first-set tiebreak but, due to rolling his ankle earlier in the game, then had no option but to retire hurt.

His retirement granted Paire just his third ATP win of 2021.

At the same event, there was also a first ever ATP win for Sebastian Baez, who coasted past Corentin Moutet 6-1 6-2 to claim a straight-sets victory.

In the Nordea Open, held in Bastad, Italian Cecchinato triumphed over former world number seven Gasquet 6-2 5-7 6-3 to reach the second round.

The 2018 Roland Garros semi-finalist, who fought off Gasquet's second-set comeback, will now face either Federico Coria or Francisco Cerundolo in the next round.

In the other first-round ties, Yannick Hanfmann recorded a straight-sets win over Thiago Monteiro, while Elias Ymer, playing in his home country, beat Taro Daniel 6-2 6-7 (6-8) 6-4.

Novak Djokovic has admitted he is still "50/50" over whether he will take part in the upcoming Tokyo Olympics due to coronavirus countermeasures put in place in the Japanese capital.

The world number one made history on Sunday by beating Matteo Berrettini in the Wimbledon final to match Roger Federer and Rafael Nadal on 20 grand slam titles.

Djokovic has won all three majors in 2021 and recently suggested he would represent Serbia at this year's Olympics, with the tennis tournament due to begin on July 24.

However, with organisers this week confirming spectators will be banned from attending events in Tokyo amid rising coronavirus cases, Djokovic is unsure if he will travel to Japan.

"My plan was always to go to Olympic Games, but right now I'm a little bit divided," he said after his sixth Wimbledon triumph. 

"I also hear that there's going to be a lot of restrictions within the [Athletes'] Village. Possibly you would not be able to see other athletes perform live. 

"I can't even have my stringer that is very important part of my team. I can't have a stringer. I'm limited with the amount of people I can take in my team as well.

"It's kind of 50-50 because of what I heard in the last couple days."

Djokovic has competed at the Games on three previous occasions, but unlike Nadal and Federer he has never previously claimed a gold medal, the bronze he won in 2008 being the best the 34-year-old has managed.

Nadal, Dominic Thiem, Roberto Bautista Agut, Denis Shapovalov, Nick Kyrgios, Simona Halep and Serena Williams have previously confirmed they will not play at the Olympics.

Switzerland's Federer, who won gold in the men's doubles in Beijing 13 years ago, has yet to make a decision on his participation.