McTominay says Mourinho "was amazing for me" at Manchester United - but added the Portuguese did give him a "serious b******ing".
"Jose was amazing for me," McTominay told The Times. "Though when I first came in Jose gave me a serious, serious b******ing.
"I was arguing with one of the first team lads in training and he said 'hey, kid, when you come into the first team, the other players - they have to like you.'
"'You're not a superstar', he said and I drove back to digs thinking 'have I just ruined it for myself? I couldn't believe it.
"I thought 'I hope he knows I don't think I'm a star, I'm the polar opposite.' He probably just wanted to see what I was made of, what sort of lad he had on his hands.
"You're liked by what you do on the pitch and how you are off the pitch and I feel Mourinho saw something in me at a time some people did and some people didn't, and I'm grateful."