Striker Marcus Rashford arrived at Manchester United's training complex on Thursday morning after sustaining a back injury in the FA Cup win over Wolves.
Rashford, who usually drives himself, was driven into United's training on Thursday, an indication he was trying to avoid further complications.
The 22-year-old was introduced as a 64th-minute substitute for Mason Greenwood but was replaced by Jesse Lingard with 10 minutes of the match to play and limped down the players' tunnel.
Explaining why Rashford was removed, Ole Gunnar Solskjaer said the England international has been struggling for a while.
"I didn't want to play him. I think he got a knock to his knee in his back, but he's been struggling for a little while, that's why we've kept him away today.
"But we needed the win, he was involved in the goal - so that was a positive - but it backfired. We will do everything we can to get him fit for Sunday.
"It's football and I never complain about all the injuries we've got, that's just part and parcel of it. And Marcus has been available and fit all season, so we can't complain.
"He's a quick healer and he'll play through some pain. If he's capable if it's not a bad, bad injury."
Manchester United travel to Anfield on Sunday for a crucial English Premier League fixture, knowing a defeat will deal a major blow to their top-four pursuit.
Liverpool are unbeaten this campaign and have only dropped point in the reverse fixture against Man United.
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