United admit Fellaini has undergone wrist surgery
According to Britain's Press Association the Belgium international has had an operation to cure the problem which has been troubling him for some time.
United mamager David Moyes had hinted on Friday that surgery was a possibility.
Fellaini has also been struggling with a back injury which has forced him to miss five games since the December 4 outing against his former club Everton.
United hope Fellaini will be back for the first leg of the Champions League last 16 encounter with Olympiakos on February 25.
Fellaini has struggled to make an impact since his Â£27.5million (33 million euros, $45 million) move from Goodison Park on transfer deadline day.
He has so far failed to score for his new club in a series of ineffective performances and on Friday, Moyes highlighted the current injury woe.
"Fellaini has an injury to his back, which we hoped might have healed up but hasn't," said the Scot.
"I am going to get another scan and if it hasn't healed up then I might need to take the decision to get his wrist done as well.
"We hoped his back would be better in 10 days but he is still feeling it."
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