Mourinho believes the Premier League demands are just too great.
He told the Daily Mail: "I think the Premier League and the internal competitions create a very difficult situation for the clubs.
"Other countries, they care a lot about the Champions League. In this country the Premier League will always come in front of the Champions League. The institutions that lead the competitions make it very, very clear.
"I played semi-finals of the Champions League with an English club and had to play a crucial match in the Premier League two days before.
"They couldn't give us one more day because it was more important to have that match for Sunday morning football than to give you a Saturday fixture and some rest. (Referring to the semi-final against Liverpool in 2007; Liverpool were given a Saturday match).
"Other countries play Fridays to rest, they play Thursdays to rest. They don't play — to rest! They manage things in a way that the teams are really focused on the Champions League."