The Brazilian joined Granada in August on a season-long loan, but it was well documented that he wanted to leave United in January in search of regular first-team football.
"Of course I was disappointed (last season). I wanted to play," Pereira told Beyond The Pitch. "Every player wants to play and I was disappointed I couldn't play more minutes.
"I trusted the manager and it didn't happen as I wanted it to but that's life and I'll learn from that as well.
"Now it's different. I spoke with Mourinho and he was honest with me and that's what I like."
The 20-year-old added: "Maybe he (Van Gaal) was honest with me, but during the season a lot of things happened.
"I couldn't say he's a bad coach. I think he's a very good coach, but unfortunately he couldn't keep his word to me about that.
"I didn't play but hopefully I can play now here (at Granada) and I can have a good season."