The Belgian midfielder, 26, arrived at Old Trafford from Everton on deadline day back in September for £27.5m as new manager David Moyes look to a familiar face in order to solve his midfield problems, after missing out on the likes of Ander Herrera, Cesc Fabregas and Thiago Alcantara.
But things haven't exactly gone to plan for the former Standard Liege star, as he has struggled with form of fitness, making him a figure of ridicule amongst United fans and opposition supporters alike. There have been some encouraging displays from Fellaini, but they have been few and far between this season.
He seemed to hit a new low last week against Bayern, turning in an abject display as he was ponderous in possession, lacking ideas and just a step off the pace against Pep Guardiola's vaunted midfield, whose expertise is in keeping the ball away from the opponents.
But after missing training this morning, Fellaini has not travelled with the rest of the United team who flew out to Munich earlier today, and will miss the vital second leg as Moyes' side look to produce a huge shock and go through the the semi-finals after a 1-1 draw in the first leg.
The news of a £27.5m signing being out injured for arguably the biggest game of the season should be enough to make any fan worry, but with Fellaini that simply isn't the case. He was found wanting against Bayern last week and was largely at fault for Bastian Schweinsteiger's equaliser, and with Moyes desperately needing a big result to prove to many that he is still the right man to replace Sir Alex Ferguson, it may well be a blessing in disguise that Fellaini will miss the game at the Allianz Arena on Wednesday.