He said: "Yeah because probably they don't understand him.
"I know how to take him and how to try to pinch him when needed. But ultimately it has to come from him if he wants to go to the next level. But he can deliver.
"He loves playing football, it doesn't come across so often. He is a genius in terms of what he can produce with the ball and you can see that in every training session.
"He thinks he plays in the park, he can deliver that ball that no one else can deliver. He has got that magical sense."
Mertesacker believes his former team-mate pays for simply having an unusual personality.
"He's a different character and sometimes I struggled with that. When I approached him and said 'this is not what we do here', I thought that sticks with us longer. For him it's: 'No, that's OK, I accept that we move forward'. I was really p*****, for days and weeks.
"But he relaxes in those moments and he is fine with it. He delivers magic moments for us and also moments where you thought he can go to another level."