It's a clash befitting a Champions League final, yet Barcelona and Manchester United will tussle twice over the next nine days just for the right to play in the last 16 of the Europa League.

A result of United's dreadful 2021-22 season and Barca's surprising failure to get out of their Champions League group means two giants of the European game find themselves in UEFA's second-tier competition.

While that might suggest a hint of both being fallen giants, these two teams are enjoying largely promising seasons, with Thursday's first leg at Camp Nou undeniably intriguing.

Barca are on course to win LaLiga for the first time since 2019, while United have made significant strides forward following the beginning of a rebuild with new manager Erik ten Hag. A Premier League title challenge could yet come to fruition.

But the Europa League is where their attention turns now, and United's bid to reclaim the title they won in 2017 – the last trophy they lifted, in fact – has them facing arguably the toughest possible challenge straight away.

The absence of Lisandro Martinez for the first leg due to suspension will be a huge source of frustration for Ten Hag, which highlights just how effective the Argentinian has been in his first few months at the club.

United prepare to suffer

Xavi's spell in charge of Barcelona to this point has been a little difficult to draw conclusions from. That's not just what critics think; there are also many, many supporters who remain uncertain.

They routinely win games without playing particularly spectacular football, and that's essentially the crux of both sides of the debate. Some fans may not be enamoured with the brand of football, but Xavi is getting results.

Since the start of the first LaLiga matchday with Xavi at the helm, Barcelona have amassed 112 points in 47 games – Real Madrid, who've played a match less, have taken 104. That's the same Real Madrid who won a league and Champions League double last year.

Now, he has Barca well on track to win the title this season. Even if they perhaps don't have the same entertainment value as Pep Guardiola's vintage Barcelona, Xavi deserves recognition for the transformation he's overseen, part of which is shown in their work rate.

They are tireless.

Former Barca coach Quique Setien, now at Villarreal, highlighted this after his team were beaten 1-0 by them at the weekend.

"There is something that this Barca has changed a lot, which is without the ball," he said. "The data is there: Barca is the team that runs the most without the ball. Seems surprising, doesn't it? Robert Lewandowski is the first defender."

How does this translate into output? Well, their 210 high turnovers is second only to Athletic Bilbao (223) in LaLiga, while Athletic and Atletico Madrid (35 each) are the only two teams to convert such situations into shooting opportunities more often than Barca (32).

Barca's 324 pressed sequences is bettered by just Athletic (330) and Rayo Vallecano (328), though Xavi's side allow their opposition on average only 8.8 passes before a defensive action. This is a low for LaLiga.

Altogether, these metrics highlight just how hard Barca work to get the ball back when they don't have it, and as such it brings into focus the kind of defensive pressure their opponents' centre-backs are put under.

The centre-back playmaker

That is, of course, where Martinez becomes relevant. Obviously his presence would likely be felt even if Barca didn't press with such intensity, as he's arguably been United's most consistent and impressive defender this season purely from a 'putting-your-body-on-the-line-and-battling-for-the-cause' perspective.

Yet, it's his ability on the ball that makes him key for Ten Hag.

Martinez's importance to United in this respect was as evident as ever during the weekend win at Leeds United. Until his 61st-minute introduction, Ten Hag's men had struggled desperately with their hosts' intensity.

Leeds were ferocious in their pressing, and although left-back Luke Shaw generally did fine in Martinez's place at centre-back, United instantly looked like they had more time on the ball once those two were in their rightful positions.

Martinez was dropping his shoulder to evade attackers, pinging long cross-field passes out to the right. Granted, you could make the case Leeds were tiring, and that's potentially a valid argument, but Martinez's performance wasn't surprising. It's just how he's played ever since making the move from Ajax.

Although he only came on with 29 minutes left, Martinez's 35 passes was only bettered by five of his team-mates and no one on the pitch (minimum three passes) had a better completion rate (85.7 per cent).

His ability on the ball makes Martinez effective at helping United resist pressure. He has lost possession 173 times in the Premier League this season, but that is just 12.3 per cent of his total touches. Only 11 centre-backs (minimum 15 appearances) have lost the ball less frequently.

This is despite his passing being positive and forward-thinking in nature, which is evidenced by the fact only Arsenal's William Saliba (22) has initiated more shot-ending sequences than Martinez (16) in the Premier League this term.

United now go into arguably their biggest game of the season – until next week's EFL Cup final – without him, a match where his strengths will have possibly been more useful than any previous fixture.

But if there's one positive, the need to highlight his importance makes a mockery of those who rushed to write Martinez off at the start of the season.