The Red Devils have just two points from the past three games, but within that period the Belgian has a goal and an assist.
Fellaini was United's only signing in the 2013 summer transfer window, and did not live up to the pressure placed on him.
Former boss David Moyes has told a newspaper that Fellaini's talent was never in doubt, but the United squad was just not set up to play to his strengths.
He told The Mail: "He can perform several jobs in a team but I think it helps him to have someone like Daley Blind sitting there in that more defensive midfield role. At Standard Liege he had Defour or Witsel sitting deeper and allowing him to get further forward, and at Everton he had players like Phil Neville.
"At United last season we lacked that kind of midfielder, and while Marouane has the physical ability to cover the ground he’s definitely more effective in a game if he’s accompanied by a defensive midfield player."
Moyes' comments are in some ways tragic, because he displays a knowledge of how to get the Belgian tick, yet was simply unable to during his time at the club. He of course was the manager who signed Fellaini for United.
His words add more weight to the belief Fellaini was a last minute panic buy, without assessment of how he could make him succeed. Moyes also failed to address it by buying a holding midfielder in January.
Fellaini actually went on record as stating he could play the role himself, but it's clear already that Blind is more adept, and while Louis van Gaal signed the Dutchman because he rates him regardless, the effect he is having on his teammate is clear to see.