Mourinho believes Chelsea can afford to pay more attention to the FA Cup, due to the fact that they have an edge in the Premier League.
United had to come from behind to beat Blackburn Rovers 2-1 at Ewood Park, with goals from Rashford and Ibrahimovic.
Chelsea won 1-0 the last time they faced United in this stage of the FA Cup and Mourinho feels their 8-point lead in the EPL will give them time to focus on training for the FA.
“Probably Chelsea can only think about that (the FA Cup) because I think they are champions and they have nothing else to fight for,” Mourinho said.
“The FA Cup is something I believe is important for them. I have to play St-Etienne (on Wednesday), I have to play the (League Cup) final, I have to play hopefully another opponent in the Europa League. I have to fight for a top four position in the Premier League. I have so many things to think about.”
“The match is in one month’s time. I don’t want to be speaking about it.”