The general secretary of the world football players' union, FIFPro, has said there is "no point" hosting Euro 2020 across 12 countries this year if fans won't be able to attend matches.
"I think the question comes down to what would be the benefit of a twelve venue tournament, and there's only really a benefit to that if fans would be allowed to witness it, if fans would be able to go to stadia," said Jonas Baer-Hoffmann to SNTV.
"Is it realistic to believe that we would have substantial attendance come June and July in stadia? If that's not the case, then there's really no point in trying.
"But at the moment, I think it is very important that the different scenarios are being developed and I'm sure UEFA would."
Meanwhile, UEFA president Aleksander Ceferin reiterated his commitment to keeping the tournament as intended.
"UEFA is committed to holding EURO 2020 in the 12 cities originally planned," Ceferin said last week to SNTV.
The 12 country format was originally devised to celebrate the 60th anniversary of Europe's top international football tournament.
But the second wave of the coronavirus, which means most European countries are currently enduring renewed lockdowns, has cast doubt over whether the multi-country format is still viable.
But Ceferin added that he was optimistic the COVID-19 situation "would be very different" by the time the tournament is due to kick off on in Rome on Jun. 11.
The possibility that fans will be able to attend matches in stadia stretching from Dublin to Baku has been left open after a meeting between UEFA and representatives of the 12 host countries on Wednesday.
UEFA is currently considering various options for how the tournament will run -- which includes hosting it all in one country -- but has extended the deadline until April for countries to come up with a plan A and a plan B for fan numbers.
Each host venue is being asked to choose from four options -- full stadiums, 50% full, 33% full or empty stadiums.