To make matters worse, the Belgian has now suffered a wrist injury which looks set to rule him out for the best part of two months.
So when United took to Facebook with a message to wish Fellaini the best in his recovery, they were probably anticipating a series of positive messages from fans.
Instead, the comments were full of disparaging messages about their midfielder.
One fan, Louise Clarke wrote: "Wont be missed."
Another by the name of Joel Fellows asked: "How does your wrist affect a game played with your feet?"
He might have a point—quotes, per ESPN.co.uk, have subsequently appeared from Fellaini's Belgium coach Marc Wilmots suggesting the midfielder could feature for his country this week wearing a splint on his wrist:
He will join the squad and train on Tuesday with a splint.
As far as I am concerned, in principle he is able to play Friday. This does not mean that he will automatically play. I have not heard from Manchester United asking that the operation should be as quickly as possible.
The rest of the comments veered from calls for Shinji Kagawa to play more to a lone voice of reason from fan Ruben Garza, per the link below, suggesting that, perhaps, just perhaps, Fellaini needed more than five games before judgements could be made:
Since when did it become cool to hate on Manchester United players, Whatever happened to team and player support? Give the guy a chance. He has potential give it a little more time.
You can see the tone of the rest of the feedback on the post here.