Manchester United boss Jose Mourinho says Eric Bailly has a 'serious' injury and is not sure how long it will keep him out for.
United were again without defender Bailly, who has been out since early November with an unspecified injury, as they beat Bournemouth 1-0 last night.
Mourinho was unwilling to give details about the Ivory Coast international's problem when asked after the game but admitted he could be facing a long lay-off.
He said: "I think it's serious. We are trying a conservative treatment but if the conservative treatment is not resulting (in recovery), he will probably have a surgery procedure. But let's wait a little bit more."
Asked if it could prove a season-ending injury, Mourinho said: "I don't want to be so pessimistic."
Meanwhile, Mourinho was pleased with United's response to their derby loss as they overcame the Cherries at Old Trafford.
Romelu Lukaku scored the only goal on Wednesday as United got back to winning ways after their damaging, demoralising and controversial defeat to arch-rivals and Premier League leaders Manchester City on Sunday.
Mourinho said of his players: "I think (they had a) very good attitude, very good determination to win. I think every team, after a defeat, tries not to have a second defeat and that was in the back of their minds when they were playing.
"They wanted to win the match and I could see that from minute one to the last second."