The 20-time English champions kicked off their pre-season preparations with a 5-2 win over Los Angeles Galaxy on Saturday night, and Mourinho played three at the back in both halves of the contest.
It had been suggested that the Portuguese could look to sample that formation once again, but he has confirmed that a back four will take to the field against Real Salt Lake.
"We are not going to repeat in the next match the experience [of LA Galaxy], so players [will be] playing in different positions and thinking football in a different way, and being organised in a different way. We are also going to play with four at the back," Mourinho told Man United's official website.
"We will work with the same principle - 45 and 45 [minutes] and, if there is a chance to give five or 10 minutes to another kid, it's always good for them."
After facing Real Salt Lake, United will take on Manchester City, Real Madrid and Barcelona during the latter stages of their USA tour.