Sport BILD reports that United have launched an attempt to sign the Germany striker before the transfer window closes.
Muller has long been linked with a move to Old Trafford, but reports claim Bayern are not keen to sell the forward.
United have reportedly had two offers for the player already turned down this summer.
The Germany international is apparently keen on making a move to the Premier League giants.
Arsenal have also been reported to be considering making a move for the German forward.
