By North-west correspondent Alex Stevens

Marouane Fellaini has flown to Belgium for treatment on a suspected hamstring injury as Manchester United try to clear their 13-man casualty list, Football Insider sources understand.

The midfielder has been ruled out of United’s Europa League tie with FC Midtjylland on Thursday night after suffering what Louis van Gaal said was a muscle problem.

United are keen to get to the root of the injury and Fellaini travelled to his homeland on Wednesday for check-ups with Belgium team physio Lieven Maeschalck on a suspected tear.

Louis van Gaal confirmed the injury after United landed in Denmark although he was vague about the details.

He said: “Fellaini is injured. He has a muscle problem because he has played in a lot of matches in a row and that is difficult for him.”

Fellaini has become a regular under Van Gaal since Bastian Schweinsteiger suffered a knee injury in early January, starting 12 of the 14 matches before he missed the 2-1 weekend defeat at Sunderland.

With Wayne Rooney ruled out for up to two months with knee ligament damage, Fellaini might also be required to play up front as United attempt to secure Champions League qualification.