Leon admits he didn't get along with the Manchester United manager.
Ahead of today's clash with Real, Leon revealed: "It was an opportunity presented to me and it did not go well.
"When there is a conflict between two people, both have the fault. More so when being young, that caught me innocently. If what I know now would have happened to me at that moment, it would not have happened as much as it did then.
"I would have channeled it in another way."