Last summer the 21-year-old was selected by the newly-appointed United boss for the pre-season trip to China, only to join Granada on a season-long loan later that summer.
Taken to the United States on this summer's pre-season tour, the versatile midfielder wants to make an impression on manager Mourinho.
"I am very happy that I am back, and I can be part of this team," Pereira told MUTV.
"I will try to do my best to stay here, get an important role for the season, to help my team-mates and to impress the manager.
"It boosts me that the people here trust the young players. I am very happy for the young players and I want to be a part of this team as well."