It seems to me that even if Man U remain unchanged next season, their game shouldn't get any worse... As far as I know, the main players are not leaving the club yet... Man U showed good football last season and finished the season in third place... If they don't have any major team changes, they can continue to play well without any new transfers...
So far all I've heard is De Gea leaving. On loan Marcel Sabitzer and Wout Weghorst also returned to Munich and Burnley. Mason Mount's arrival might be an alternative option for Eriksen, Fred and Scott McTominay. It looks like Mount's arrival will be pushed ahead of Casemiro alongside Fernandes, Mc Tominay. In addition, maybe the injury factor makes Ten Hag Hag want to have a lot of creative midfielders.