Ole Gunnar Solskjaer said on Sunday captain Harry Maguire could be out for a "few days or a few weeks" after he picked up an ankle injury in Manchester United's 3-1 win over Aston Villa on Sunday.
The England international was taken off late on after colliding with Anwar El Ghazi before United went on to claim three points to keep their very slim title hopes alive.
Solskjaer says it is unlikely Maguire will play against Leicester on Tuesday night and admits he may not play at all this week.
Man Utd agree fee for Sancho - report
"The boy [El Ghazi] landed on top of him and he twisted his ankle," Solskjaer told the club's official website.
"Harry has been excellent and it’s almost unheard of, the minutes he’s played without missing him.
"We’ve a [Europa League] final to look forward to and hopefully it will be with Harry; it might be a few weeks, it might be a couple of days, we don’t know. Hopefully it won’t be too bad, but I’m not a doctor, and we’ve got to scan him on Monday.
"He may be available on Thursday [against Liverpool], but I don’t know, it might be longer. I’ll tell you more on Thursday."
- Sergio Aguero delays Man City's title for another week - The Warm-Up
- Real Madrid plan to use Hazard as pawn in Mbappe bid - Paper Round
Manchester United are on a run of three games in five days. After Leicester on Tuesday they play their rearranged fixture against Liverpool on Thursday.
Maguire wrote on Instagram: “Important win. Hoping the injury is nothing serious and I'll be back playing soon. Thanks everyone for your messages.”
On Monday Solskjaer said he would ring in the changes against fourth-placed Leicester with several of the club's academy players set to feature.
"They're training with us every day so... some of the young boys will get an appearance," he said.
"If it's coming on towards the end or starting I don't know because I don't know how the players will be on Tuesday.
"I wish I could have said let's go full out in all the games. But it's impossible. That's the hard bit for me - knowing that if I do play the same eleven again on Tuesday and Thursday, it's impossible," Solskjaer added.
"I run too much of a risk of injuries so talking about integrity in the league and stuff, don't blame me when I have to make changes, because I have to. It's not safe... I've got to prioritise."
United lead chase for Varane but Real remain stubborn - report
'Dramatically bad' - Mourinho blasts England's set pieces and 'poor' Shaw