Centre-back Eric Bailly, injured while on international duty, is set to go under the knife for his ankle urgery.
The Ivory Coast defender has missed last 8 games for United, last featuring in the 1-0 defeat to Chelsea on 5th November.
Baily came back from international duty in October with a groin injury, and returned for United two weeks later in the 1-0 win over Tottenham. He started the following games against Benfica and Chelsea, but suffered another injury during the November internationals, even though he was suspended for the Ivory Coast’s final World Cup qualifier against Morocco.
“I think it is serious. I don’t know [how long he will be out],” Mourinho said.
“We are trying a conservative treatment but if the treatment is not resulting then probably it will end in a surgical procedure but let’s wait a little bit more.
“Today, I played [Chris] Smalling and [Phil] Jones and we had [Victor] Lindelof and [Daley] Blind on the bench. Marcos Rojo was injured [against Manchester City] but nothing really big.
“During the whole season, we’ve had problems with central defenders but, because the number is four or five, we manage always to have [players available].
Despite United’s impressive defensive form this season – with just 11 goals conceded, the joint-least in the Premier League along with Manchester City – Mourinho has yet to find a reliable centre-back pairing since arriving at Old Trafford in 2016.
United not sure if Bailly is out for the season
Mourinho started Chris Smalling and Phil Jones for Wednesday’s 1-0 win over Bournemouth and following that win, the Portuguese boss said he was happy with his options at centre-back.
“Chris Smalling is playing amazingly well for seven or eight matches in a row maybe, so we are fine.”
“I don’t want to be so pessimistic [as to say he might be out for the season]. I want to leave it with a doctor. I’m not a doctor. There’s nothing to hide, but I don’t want to be speaking about it
They trail Manchester City with 11 points and will be looking to close the gap on their rival when they clash with West Bromwich Albion on Sunday.
Bailly was the first player to sign for United after Mourinho took over as manager, joining from Villarreal in the summer of 2016 for £30m. Manchester United have conceded only 3 goals in 8 games when the 23-year-old has started, and have faltered to 8 goals in 9 matches when he was injured.
Bailly played a huge role in Mourinho’s defensive tactics. United were hopeful that he will respond well to the treatment but he eventually needs to undergo an ankle injury. The extent of the Ivorian’s injury means he could potentially miss United’s Champions League knockout ties\ with Sevilla and the Carabao Cup final, should they progress that far.