United booked their place in the last eight with a narrow 2-1 win over Blackburn Rovers at Ewood Park this evening, but were handed arguably the toughest available draw afterwards - an away trip to the Premier League leaders.
With an eight-point lead at the top of the table thanks to recent Premier League scores, Mourinho believes that Chelsea have already wrapped up the Premier League title and can give their full attention to the FA Cup due to their lack of European football.
"Probably Chelsea can only think about [the FA Cup] because I think they are champions and they have nothing else to fight for," he told reporters.
"The FA Cup is something I believe is important for them. I have to play Saint Etienne [on Wednesday], I have to play the [EFL] 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."
United lost 4-0 on their most recent visit to Stamford Bridge in October.