The France international became the world’s most expensive player when he re-joined United from Juventus in August but he has failed to regularly hit the heights while being shunted to and from a variety of midfield roles.
Manchester United face rivals Manchester City in the fourth round of the EFL Cup on Wednesday as they aim to bounce back from a chastening 4-0 loss at Chelsea, but Mourinho is talking a long-term view over his marquee acquisition.
“He can play in so many positions,” he said in an interview with Sky Sports. “The problem is not the position. The problem is not the tactical system.
“The problem is, in my opinion, somebody that comes from a different style of football and needs this time to be at his best level in football that is really difficult to play, especially for midfield players.
“I think it is really difficult to play or adapt from different realities, but he is a phenomenal player. He has unbelievable potential.
“He has years and years to develop his game, so that expectation and investment from the club is based on that – a super player for the next seven or eight years.
“He’s getting better and better and better at every level. That’s our expectation. We don’t expect Paul to arrive here and the next day to be unbelievable. But the other thing is that we trust him so much that we pass to him this kind of feeling.”