The 20-year-old barely featured throughout Man United’s pre-season and was an unused substitute in their 1-0 defeat to Arsenal in their first Premier League game of the season.
Mainoo is still highly regarded at Man United, although the appointment of Amorim has seen chances lessen for the England international.
Speaking to the press ahead of their game against Fulham on Sunday (August 24) Amorim took responsibility for Mainoo’s issues.
Amorim said: "We had some issues but we play with two midfielders, so it’s sometimes a different way of playing, and we have to understand, they have to understand, especially the young players, that there is phases in the season.
“Nowadays it’s normal with a lot of games, things are going to change, but he is there, he’s fighting, he’s training, so he’s one more option for us to win games."