"I can only say a huge thank you because I learned so much from him," Fellaini said.
"When I arrived at Everton he spoke to me about English football, the life and the style of the country. Also at Man United he spoke to me about life there as well. It is important because we have football but we also need a life as well.
"I played a lot of games for Everton and had some very good moments there. I could never say something bad about him because he has done everything for me. When I played bad he told me. When I played well he told me. When I have a bad demeanour on the pitch he tells me.
"When it's bad off the pitch he tells me that as well. It's important for me that when I am good he tells me. And when I am bad he does the same.
"Last season when I was suspended for Stoke City [after a headbutt] he was very hard on me. He made me go back out and train alone with him. I was like his son and I had been bad so I took my punishment."
Fellaini added: "He is the most important person in my career. I could never say something bad about him because he has done everything for me.
"He has done so much or me that of course I want to repay him at Manchester United."
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