Consecutive home defeats have seen the Red Devils fall to ninth, 13 points behind leaders Arsenal, but Mourinho said that there is still time for them to get back into the hunt.
"I think it's going to be difficult for them," BBC Sport quotes Mourinho as saying. "It's not just because they're 13 points behind Arsenal but also because they're eight points behind us and Liverpool, and seven behind Manchester City.
"So United have to recover points not just to a single team but other teams. But the culture of Manchester United is there, and the power and tradition is there. Never say Manchester United are out of the race unless it is mathematically possible."
Mourinho's Chelsea take on Crystal Palace on Saturday.