Head coach Rúben Amorim confirmed that Mainoo suffered a small calf injury in training just before the game. The problem means he was not fit to play or even sit on the bench at Villa Park, even though some supporters thought he might get a chance in the starting lineup.
Before this setback, Mainoo had been waiting for more regular playing time this season. He has not started a single Premier League game so far, and his role under Amorim has been limited mainly to substitute appearances. With other midfield players like Casemiro suspended or unavailable, many expected Mainoo to get a chance, only for the training injury to rule him out.
There has also been transfer talk linking Mainoo with a move away from Old Trafford in January, with clubs like Napoli reportedly interested, but Amorim has pushed back against the idea that the midfielder’s squad absence was due to unhappy feelings or transfer issues. Instead, the manager said the decision was simply because of the calf problem and not because of anything off the pitch. 
Amorim also used the conversation as an opportunity to encourage Mainoo to focus on his game and fight for his place in the team. In press comments, he pointed out that being young and spending time on the bench is not unusual — even legendary players sometimes had to prove themselves before becoming regulars.
The injury comes at unlucky timing for the 20-year-old, who had impressed when coming off the bench in recent matches. While Mainoo’s future at the club continues to be discussed in the media and among fans, the immediate reason he missed the Aston Villa trip was purely because of the calf injury suffered in training.
