In a fans Q&A, McTominay revealed Fletcher was always welcome in training after his appointment last season.
He told manutd.com: "Darren has been absolutely amazing whenever he's come in, he's been a breath of fresh air. All the lads have really taken to him. He was a proper player and is a proper football man. Michael Carrick, the manager, Mike Phelan, are all men who know the game inside out with vast experience of many different leagues.
"For myself, it's brilliant that I've got some of the best guys I could possibly wish for to help me with my game. I have to soak it in and maybe one day, be in a position like that and can say I was learning from them and the cycle continues."