The Red Devils brought in Aaron Wan-Bissaka, Daniel James and Harry Maguire over the summer.
And McTominay has been impressed with the trio's work on the training pitch.
He told the club's website: "Yeah, they've slotted in really, really well and that's part of it whenever you come to a football club like Manchester United. You have to have that personality to come into the dressing room and own it.
"You have to come in and show people that you should be there and that you are going to be there and you are going to play and you want to show everybody including the staff and players that you are there for the long run and you're not going to be a bit quiet and ease your way in.
"These boys have come straight in and they've played so, so well so far and it's a credit to them and a credit to their previous clubs for their education that they've had."