Eric Bailly could require surgery on an ankle issue that Manchester United manager Jose Mourinho thinks might be "serious".
The defender has not featured for United since the 1-0 defeat to Chelsea on November 5, having sustained a problem while on international duty with the Ivory Coast.
Reports this week suggested Bailly may be out of action until next year, and while Mourinho could not confirm how long the 23-year-old is set to be sidelined, he suggested the absence could be long term.
"I think it's serious," Mourinho said after United scraped a 1-0 victory over Bournemouth on Wednesday. "I don't know [how long he will be out].
"We are trying conservative treatment, but if that's not working he'll probably have surgery.
"It's an injury that comes from the last time he went to the national team, and then we are trying the conservative treatment but if the conservative treatment is not resolving, he might have a surgery procedure, but let's wait a little bit more.
"I'm not a doctor, probably the doctor can inform, is not a problem for me, I just don't want to speak about it."
Bailly, who joined from Villarreal in June 2016 for a reported £30million, was out of action for over a month last season after sustaining a knee ligament injury in October last year.