Bruno Fernandes is in danger of missing Manchester United's Old Trafford showdown with Liverpool on Sunday through injury.
Portugal playmaker Fernandes is among several United players feeling the effects of Wednesday's pulsating Champions League contest against Atalanta.
Manager Ole Gunnar Solskjaer confirmed some players had to sit out training on Friday, little more than 48 hours before United seek to halt their Premier League slide against bitter rivals Liverpool.
"Games like Wednesday night are always going to bring knocks and bruises," Solskjaer said at his pre-match press conference.
"We do have two or three from that game. Bruno might be one of them that is a doubt, but he's doing everything he can to be ready."
Fernandes' importance to United is evidenced by him scoring 30 goals and having 21 assists in 59 Premier League appearances since arriving from Sporting Lisbon in January 2020.
Fred and Marcus Rashford also picked up knocks against Atalanta and were forced to leave the field.
England striker Rashford, who was making his first start after a shoulder operation, suffered a dead leg after scoring United's first goal in the 3-2 comeback victory.
Solskjaer said: "It was a great effort towards the end of course - a great comeback and a great Champions League night.
"We have some knocks and bruises. But it's still Friday, the game's on Sunday, and we will give everyone time.
"Today (in training), we didn't have everyone, but let's see Sunday.
"I hope I can pick from a fully fit squad. It might be that I'm without two or three."
On Brazilian midfielder Fred, who has often found himself the target of critics, Solskjaer said: "He is a very good player and a regular for Brazil, which in itself is a mark of quality.
"He has got an exceptional personality and attitude to football, such a big smile.
"I can't say at the moment whether he's going to be fit or not, but he'll give everything he can to be there for us.
"He got injured at the end of last season and it was supposed to be a six-to-eight-week injury.
"But he was back the day before the Europa League final. He was fit and fully joined in the training session.
"We had to strap him up for the game but if I'd known before maybe I would have played him. He would have put his hand up and sacrificed himself for the team, that's for sure."
While Wednesday's win put United top of their Champions League group, Solskjaer's side have taken only one point from nine in the Premier League.
United lost to Aston Villa at Old Trafford and were held at home by Everton, before last weekend's late collapse at Leicester saw them lose 4-2.
That run has left them five points adrift of leaders Chelsea and four behind Liverpool, the only unbeaten side in the division.
Liverpool are the Premier League's top scorers with 22 goals in eight games and almost certain to punish the sort of careless defending United were guilty of on Wednesday.
Solskjaer said: "A performance needs to consist of 90-plus minutes of attacking and defending against a team the level of Liverpool.
"At the moment they are on a great run of form with some individual skills that you cannot almost defend against, but as a team we have to be compact and aggressive.
"It's going to take everything to get a result against one of the best teams in Europe and the world - and Liverpool are one of those.
"They are one of the teams we are trying to chase because what they have done in the last four years is something we are striving towards and go past them.
"We did end up above them last season, but they had a very bad spell of injuries and now they are back to their best."