Dan Biggar fears a "huge step backwards" if there are no crowds allowed at matches moving into 2022.
While crowds at sporting events have yet to be capped in England, matches in Wales and Scotland are now limited when it comes to capacity, amid a sharp rise in coronavirus cases.
Wales' first minister Mark Drakeford has not put any timescale on when the restrictions will be lifted, with the Six Nations set to start on February 5.
Scotland will formally review their measures on January 11, while France – where over 18,000 people were in hospital with COVID-19 as of December 30 – has imposed restrictions on travellers from the United Kingdom, with their government insisting that all sportspeople must be fully vaccinated by mid-January in order to enter the country.
Italy, likewise, is experiencing unprecedented levels of new recorded cases of the virus as the Omicron variant spreads across Europe.
But Wales fly-half Biggar believes banning spectators would be a frustrating move that will only damage the game.
"It would be a huge, huge step backwards if there are no crowds moving forwards for clubs and the Six Nations which is obviously such a showpiece event," he told reporters.
"You saw it in the autumn, getting crowds back. Everyone coming to games now has to have a passport, they'll be double or triple-jabbed, and it's an outdoor event so I don't see why they wouldn't be allowed in.
"As long as it's safe, that's the most important thing.
"I hope for an event like the Six Nations and for the game up and down the UK moving forward we get some sort of sensible outcome.
"As long as everyone is safe and jabbed then I think it makes sense to keep crowds in. I think you would have seen a different [Northampton against Harlequins] game if the stadium had been completely empty.
"We played a lot of games with no crowds but if you look at the first handful of games they almost felt like training games.
"It felt like it did not really matter whether you won or lost because it felt like a training match and like the intensity was knocked out of it. You lose any advantage of playing at home and bits and pieces like that.
"I think it would be a huge step backwards if crowds were to go. I think the rest of the lads in Wales are pretty frustrated with it. That's normal frustration isn't it?
"We are probably getting into different things with politics now but I think everything should be aligned."
Wales, the defending Six Nations champions, start their campaign against Ireland on February 5, with their first home game scheduled for February 12, against Scotland.
Ex-All Blacks coach Hansen fires 'chokers' warning to Ireland ahead of World Cup
Former New Zealand coach Steve Hansen warned in-form Ireland they still have a huge point to prove at the Rugby World Cup this year.
Andy Farrell's side completed a Grand Slam against England on Saturday, sealing a Six Nations crown and reaffirming their place as the world's number one team.
But with France 2023 looming in just under half-a-year, they will have to overcome their own history, having never progressed beyond the quarter-final stage.
Hansen, who knocked Ireland out in the last eight with the All Blacks four years ago in Japan, feels they must defy their own tournament reputation to triumph.
"They are going well, [are] ranked number one in the world, and they have had a great year so far," he said.
"Every time a team is number one in the world, you have got to consider them to be a World Cup contender. But it is a tough tournament to win.
"They have seemed to struggle a little bit at World Cups. If it was the All Blacks, they would probably be called chokers. They have come a long way, they believe in themselves. They are a very good side.
"So they are definitely a contender. But they will have to overcome the pressure of not having gone past the quarter-finals before, and there will be a lot of pressure involved in that.
"If they get through to the semi-finals, then they are in new territory. That is something they will have to deal with that they've never dealt with before, and it is always hard to deal with something you haven't dealt with before."
Ireland open their campaign against Romania on September 9, before they face Tonga, Scotland and reigning champions South Africa.
Farrell warns Ireland have 'a long way to go' to reach their peak despite Grand Slam triumph
Andy Farrell believes Ireland have "a long way to go" before reaching the peak of their powers despite winning the Grand Slam.
Ireland were crowned Six Nations champions on Saturday after beating England 29-16 at the Aviva Stadium.
Farrell's side are top of the rankings following 10 consecutive victories and will be expected to mount a strong challenge to win the Rugby World Cup for the first time in France later this year.
Yet the Ireland head coach is demanding more from his players after they celebrated a fourth Grand Slam triumph.
"I said to you in New Zealand, 'now this was the start of our World Cup year'," Farrell said.
"The most pleasing thing is that we've continued to be successful. To find a way. Everyone was nervous about that except us.
"This is part of the journey, isn't it? Obviously this stands on its own right, as does the New Zealand tour.
"But it's part of the journey of us as a group going forward into a World Cup. Like I said, we'll get two or three months pre-season training for the first time together and I expect ourselves to be better obviously because of that.
“We've carried on winning, is that the yardstick? I don't know.
"We just go on the performances and the performances were pretty good in New Zealand and we've continued to again find a way.
"It's never been perfect, but the game is not like that, so the mental strength of our game and large parts of our game are in a good place.
"There's a long way for us to go for us to be at our best which is a great sign."
Borthwick 'can't do anything about the past' as England plot post-Six Nations success
Steve Borthwick says he "can't do anything about the past" with England, but the coach is looking forward to a lengthy World Cup build-up after their Six Nations efforts.
The former Leicester Tigers boss took the reins of the national team from Eddie Jones in December, less than a year out from the showpiece tournament in France.
With England having struggled at the end of 2022 under the Australian, Borthwick was unable to completely reverse the rot in a Six Nations campaign that ended with a 29-16 loss to Ireland.
But with just under half a year until they open their World Cup account against Argentina, he intends to use his first taste of the job to put their recent ghosts firmly out of mind.
"We'll debrief this Six Nations thoroughly, take what lessons we take from it and be clear on our direction going forward," he said.
"The team is not where it could be and, while we're judging against teams that have used this four-year cycle tremendously well, that's not the position England are in.
"I can't do anything about the past. I intend we will be working really hard to put England in the best position possible, and I'm excited about what these players can do for the World Cup.
"We get a number of weeks to prepare. Players will then be conditioned for international rugby and understand how we want to play.
"This has been five intense games, and effectively you then have one main training session a week.
"I'm looking forward to having the opportunity to work with the players for a longer period of time. I think we've seen some growth here, but we will see more in that preparation period."
In addition to facing Argentina, England also play Japan, Chile and Samoa in Pool D later this year.
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