The Portuguese played the full 90 minutes of the Red Devils' 3-2 win over Atalanta in the Champions League on Wednesday night, however, he was on the end of some tough tackles.
He went to United's Carrington training ground on Thursday for a warm down session with the rest of the team, but The Sun report he was limping heavily after the extent of his exertions caught up with him.
It's claimed manager Ole Gunnar Solskjaer will assess Fernandes on Friday ahead of the game, but it would be a huge blow if the 27-year-old is unavailable for Sunday's clash at Old Trafford.
Fernandes played his role in the Red Devils' stunning comeback win in the Champions League, providing assists for two of Man United's goals and earning the Man-of-the-Match award
Solskjaer was given huge credit by talkSPORT's Jamie O'Hara as Man United came back from 2-0 down at half-time to claim the three points.
O'Hara said on the Sports Bar: "Credit where it's due, Ole Gunnar Solskjaer pulls it out the bag again. He must've been going in at half time thinking 'I'm on my last legs here, I'm done, I can't keep my job.'
"But the players come out and dig him out of a hole again!
"That says something about him as a manager when the players come out and put in a performance like that in the second half."
However, Jason Cundy insists Solskjaer's side need to stop getting into situations where a heroic comeback is required.
The former Chelsea defender said: "I've never seen a team so consistently be brilliant and shockingly bad in the same 90 minutes - sometimes in the same 45 minutes.
"I don't get them as a side - they're ridiculous. They can be so good and so bad in the same game with the same players. Remarkable.
"Every time Solskjaer needs a result… as bad as United can be like they were against Leicester… they can't keep getting away with it, but they do.
"Somehow they can be dreadful, give teams a two-goal head start - like Southampton last season when they were 2-0 down, Villarreal this season.
"They're a Jekyll and Hyde side. From shockingly bad, pathetic at times, to absolutely brilliant. I can only imagine what it was like at half time."
United can ill-afford to give Liverpool a two-goal head start…