The Dutchman is sceptical about Mourinho's chances of repeating the success he enjoyed in his first Chelsea spell when he led the club to back-to-back Premier League titles.
He told Sky Sports: "They asked me four months ago what I thought about Mourinho coming back and I already had my doubts about it because it's not easy to do the same thing twice.
"I had my doubts also because at Real Madrid he didn't manage to do the things that made him so strong - and that's man-management.
"He had a difficulty there and for that reason he tried to create a war that he could not win. He acknowledged that in the end and Chelsea was the way to get out of there. But can you do it again? It's difficult.
"He is not there to nurture; he is there to win and nothing else. He wants to win and he is eager to win and has the same drive.
"But can you do it? Everyone knows him now. Everyone knows all the tricks that he makes to try to wind the opposition up.
"Also the Premier League has changed. More teams are there to win the title, so for that reason it's more difficult than it has ever been."