Manchester United midfielder Scott McTominay sustained suspected knee ligament damage in the win over Newcastle United, manager Ole Gunnar Solskjaer says.
McTominay, 23, suffered the injury after making a block tackle on Matty Longstaff early on in the 4-1 victory.
The Scotland international was replaced by Paul Pogba at half time.
"He's done his knee ligaments probably," said Solskjaer. "I don't know how bad."
McTominay left Old Trafford on crutches and is now a doubt for Saturday's trip to Burnley.
"The boy has got the biggest heart and we've seen him heal quickly before but I am not sure if he is going to be ready for Saturday," Solskjaer added.
McTominay has played 21 times in all competitions for Manchester United this season. He was booked in the win over Newcastle after just 24 seconds - the quickest yellow card handed out since statisticians Opta began collecting exact time data in 2006-07.
Solskjaer's side fell behind in the match but goals from Marcus Rashford, Mason Greenwood and two from Anthony Martial sealed victory.