The summer signing said that he received advice from the former England boss during the international break.
The advice in question? Don't lose your head, was the underlying message from a manager who has already seen the new boy red carded in front of his home fans.
Mitrovic said: "He said to play good football, that he hoped I scored and to stay calm. I sent him one back saying thank you. I speak to him a lot, really. I speak to him almost every day. He [tells me he] believes in me and that is really important."
Did he score? Like much McClaren touches at the moment, the prompt was unsuccessful - but perhaps the disciplinary message is getting through, even if his fiery streak will always remain.
Serbia had two players sent off in their home defeat to Portugal, but Mitrovic was not one of them, instead it was Premier League duo Branislav Ivanovic of Chelsea and Aleksandar Kolarov of Manchester City.
Mitrovic insists his early sending off against Arsenal was a result of being too eager to impress, and feels he has calmed now and can play his best football, as demonstrated with his strike against Chelsea.
He said: “I had a big problem in the first few games. I think I wanted to show everything in just one game. I had to show everyone that I would give everything. I played more with my emotions than with my head.”