I don't entirely feel that DM is to blame for this. There are a number of factors involved.
But perhaps the biggest criticism towards him, is the lack of confidence he inspires in that United team.
Opposition teams feared playing United, home or away, largely because of Fergie. DM just doesn't inspire the same sort of fear in the opposition, and probably not the same level of confidence in his squad. If teams don't fear United at OT, what will happen when they have to visit other teams? He needs to be careful that the team doesn't develop an inferiority complex due to the results. Fergie, to his credit, was the master of hammering the opposite attitude into the team.