It seems that Manchester United under Amorim will make a major overhaul of their squad after struggling in the last two matches, even though they have changed coaches, their performance has not completely improved from before. Amorim will rebuild his squad if Manchester United sells half of the current squad, some names are still very much needed such as Amad Diallo, Kobbie Mainoo, Mazraoui, De Ligt, Leny Yoro and Andre Onana.
If this breakthrough really happens, Manchester United will be very busy in the transfer market.
It is normal for a new coach to overhaul the team because he needs to work with players he is comfortable with especially if they are performing poorly. Manchester United has enough quality players but he still needs to get player he understands better. Ruben Amorim once hinted that he would not bring any player from Sporting Lisbon this January which shows that he might go for many of them at the end of the season. If this breakthrough really happens, Manchester United will be very busy in the transfer market.
To avoid having too much players in the squad, I would have advised that he manages the available players until the end of the season. This is because he might not be able to offload all the players he doesn't want. Some clubs might not be willing to pay enough money for such players and don't forget that the club needs to balance their book to be in line with the financial fair play.
But if I were in their shoes, I would sign a LW instead of parting ways with Rashford. A really reliable one I mean. 
