Ajax have become the latest Champions League club to be hit by coronavirus with 11 players testing positive ahead of their tie against FC Midtjylland, according to Dutch reports.
The club have not disclosed the names of the players and it is currently unclear if Wednesday's meeting will go ahead despite Ajax - third in Champions League Group D with one point from two matches, five points adrift of leaders Liverpool and three behind Atalanta - naming a reduced 17-man squad for the trip to Denmark.
Ajax players were tested on Monday and the club had been in discussion through the day with various authorities about who could travel to Denmark.
Manager Erik ten Hag said he was hopeful some of those left behind might be allowed to travel on Tuesday to join up with the rest of the squad as Ajax look for their first win in Group D.
"There are few players who can play in the Netherlands but did not get permission to enter Denmark and its a bit strange," he said.
"They have no symptoms or complaints. If they might still be able to play rests in the hands of the medical personnel and the authorities. I have strong hope that they can play but I am not sure."
Ajax's match against FC Midtjylland - bottom of Group D having lost their first two games - is not the only game affected, with Bayern Munich confirming defender Niklas Suele tested positive for coronavirus and is currently self-isolating on the eve of their Champions League match at Red Bull Salzburg.
Ajax's 17-man squad to face FC Midtjylland
Scherpen, Schuurs, Mazraoui, Blind, Martinez, Tagliafico, Klaiber, Timber, Alvarez, Ekkelenkamp, Neres, Antony, Promes, Traore, Huntelaar, Brobbey, Jensen
The 25-year-old Germany centre-back is the second Bayern player to be pulled out of action after Serge Gnabry's false positive test in October. Gnabry has since returned.
Bayern, who won five titles in 2020 including the Champions League and the domestic league and cup double, travel to title rivals Borussia Dortmund on Saturday.
Spanish champions Real Madrid, bottom of Group B, have also been hit with defender Eder Militao testing positive for Covid-19 ahead of their home game against third-placed Inter Milan on Tuesday.
The club added that all other first-team players and coaching staff, as well as the club employees who work directly with them, had tested negative both on Sunday and Monday.
Meanwhile, six Dynamo Kiev players and five members of staff have tested positive before Wednesday's Champions League Group G game against Barcelona in Spain, the Ukrainian club confirmed.
"Testing showed a positive result in several players of the team: Georgy Tsitaishvili, Denis Garmash, Mikkel Duelund, Alexander Karavaev, Tudor Belutse and Mykola Shaparenko," Dynamo said in a statement.
"In addition, the tests of assistant head coach Emil Karas and four representatives of the team's staff gave a positive result."
Dynamo are third in Group G with one point, five behind leaders Barcelona.
Tadic, Onana, Klassen out of Denmark trip
Ajax skipper Dusan Tadic, goalkeeper Andre Onana and midfielders Davy Klaassen and Ryan Gravenberch were all expected to start the Group D match at Herning but were left out of the travelling party.
Reserve goalkeeper Maarten Stekelenburg has also been omitted, leaving one keeper, Kjell Scherpen, for the trip.
Coach Erik ten Hag is due to hold a news conference later on Monday.
Dutch media said secondary tests were being conducted on Monday for those affected in the hope that the results might turn out negative and more players would be able to travel to Denmark but they would need permission from UEFA to do so.
Under the rules of Europe's football governing body, Ajax must play the game if 13 or more first-team players are available.