McTominay, speaking after United beat Southampton 1-0 on Saturday, was asked about the Reds' new signings and he lavished the praise on Casemiro and Lisandro Martinez, who started alongside Raphael Varane at centre-back at St. Mary's stadium.
The 25-year-old explained that Casemiro, in particular, has impressed United's dressing room in training this week.
"We have to make sure the team spirit keeps lifting," McTominay told MUTV. "The guys that we've brought in, Casemiro and Lisandro [Martinez], they're doing an amazing job in training, obviously we just want them to settle as quickly as possible.
"To learn from someone like him [Casemiro], who has done pretty much everything in the game, is amazing. His mentality, the way that he is so firm with everything that he does. He's an amazing footballer who can help us so much and be one of our main players.
"It's great to have him, we love him and Lisandro, Tyrell [Malacia] as well. The guys that we have brought in are doing a great job and long may that continue."