United are currently five points clear at the top, though they must visit the second-placed Gunners on May 1.
Mulumbu told The Sun: "I think it will be very hard now for Arsenal. They have dropped a lot of points.
"I feel Manchester's team is too solid to let this championship slip.
"I think the title is already over and that Manchester will win it.
"It comes down to mentality. Manchester are very strong. In a game like Saturday's, I think they could come back and equalise and then win the game. I believe that's what Arsenal is missing a bit.
"I would say that's their downfall. The youth and the enthusiasm they have but, unfortunately, they do not have the mentality that Manchester possesses."
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