The mistake at MU has shifted from midfielder Harry Maguire to goalkeeper Andre Onana this season.
You have a point because one of the major issues with Manchester United is there midfielder and goalkeeper, although in times Manchester United goal goalkeeper, De Gea was just the goalkeeper that really understand the actual pattern of Manchester United I don't no why they decided to sold him when there problem was not from the goalkeeper but I believe they now understand how important De Gea was to the club.
Casemiro has been performing more than enough for manchester united and i can't agree if you say that if the main problem was on the midfielder and defenders. I think that we shall put focus into the defenders rather than goalkeeper.
Manchester united needs to put its focus into the defenders instead of midfielders. So many times manchester united conceded so many goals due to the inconsistentcy from the defenders.
I think that manchester united needs to identify the major problem first.
and even there current goalkeeper Onana is not helping Manchester United at all, but considering his performance on AC Milan I was even thinking his performance on Manchester United will be same as when he was at AC Milan but it was quite the opposite, but however if Manchester United should work on there midfielder there could be more chances of getting back to there former performance.
I think that you are wrong here. Onana would be able to perform better if manchester united defenders were also able doing the same. It will be a disaster for the club if the defenders are still playing so badly.
Manchester united will be facing very hard fixtures and MU needs to prepare itself.