Mourinho was fired in December after a terrible start to his third season in charge at the club.
But Mitchell, currently on loan at Hearts, has refused to say a bad word about his former manager.
"I have to pay respect to Jose. He gave me my United debut so he has been an important figure in my career. He took me on tour twice with the United first team and I learned a lot under his management," Mitchell told theDaily Record.
"He's a good person. He's not always how you see him portrayed in the press. Behind closed doors, you get a totally different character."