Cristiano Ronaldo has emerged as an injury doubt for the Premier League match between Manchester United and West Ham on Saturday.
The Portugal star played 71 minutes of the 3-1 win at Brentford on Wednesday before being substituted - a decision with which he was clearly annoyed.
Interim manager Ralf Rangnick insisted he had no problem with the player becoming frustrated at going off and that it would not affect his chances of facing the Hammers at Old Trafford.
However, Rangnick later confirmed Ronaldo suffered a neck injury during the victory over Brentford that could keep him out of the game.
"Cristiano is a question mark because he has a problem with his neck," he said to MUTV on Friday.
"He received treatment yesterday [Thursday] for two, three hours and we will have to wait to see how he feels today."
Edinson Cavani missed the match at Brentford Community Stadium and he too is facing a race to be fit for the visit of David Moyes' men.
"Edi hasn't been training with the team yet and will hopefully resume training today and then we'll take the final decision after the training session, [around] if he will be available for the game," Rangnick said.
Losing Ronaldo and Cavani presents United with a possible striker shortage given Anthony Martial is attempting to secure a move away from the club.
Rangnick left Martial out of the 2-2 draw at Aston Villa, saying the France international had told him he did not want to be involved – a claim Martial later disputed.
Jesse Lingard will be available to face the club for whom he excelled on loan last season, while Jadon Sancho, who missed the Brentford match due to a family funeral, could be involved.
"We need to see where Jadon stands," said Rangnick. "He didn't train yesterday. As you know, he attended a funeral on Wednesday and didn't want to train yesterday as he is still affected by that. We will have to see.
"I will see him for training today and speak with him after the training session, to see if he is in the state of mind, and also his energy [is there], so he can be available for tomorrow."
Aaron Wan-Bissaka will also be missing again with illness, while Victor Lindelof will sit out the game after a burglary of his family home, but midfielder Scott McTominay hopes to be involved after battling a back problem.