That was terrible news for Manchester United at this moment of their poor performance. Mainoo is an important player for Manchester United, even though they have lost points this season, Mainoo has improved their performance since the previous season, so he might be in good shape by the end of next month. However, the absence of Kobbie Mainoo did not affect their performance in their last match against Brentford, Manchester United was losing in the first half and then made an impressive comeback by scoring two goals to win the game, but this doesn't mean that Manchester United is in good form because Brentford is an average team in the league.
What you said is very right because I also still see that Manchester United are not in a very good condition because they still have to improve their way of playing in other matches so that there is an increase in points and their position in the standings so that it will be considered a good thing for improving performance. But for now Manchester United still haven't done that even though they were able to win at home when hosting Brentford which is a team that is not competitive enough in the League this season.
Although still young, Kobbie Mainoo has taken his teammate's position as the main starter, unfortunately he had to sit out due to a hamstring injury. However, in the match against Brentford, Eriksen and Casemiro performed quite well as a double pivot. If United's players can be stable, especially the midfielders, they should be able to continue on the right track to get full points from match to match. Indeed, it is difficult to predict the performance of Manchester United's players, they often play underperform, like a team that has lost direction and spirit. Maybe a victory over Brentford could have a big influence on raising the motivation, spirit and mentality of all United players. Ten Hag's job is to do it, and keep his team on the right track. We'll see when Manchester United visits Turkey, visiting Fenerbahce's headquarters. If the Europa League match is important for United, getting full points should be their target. In addition to maintaining the consistency of the players, victory after victory can add enthusiasm to move on the right track.