If a new manager takes over as head coach of Manchester United now, many of the current players would be dropped to the bench and new signings made.
A player like Rashford needs to regain form to even feature in the first eleven, as well as Anthony.
The squad sure needs a better manager and although Zidane would have been a good option, I think he would do better in development of french league football or somewhere in a Spanish team. He just can't have it learning how to speak English again and building a team from a place where politics and favorites get to be regular starters compared to talent and form.
The new coach surely will do that sooner or later, to create a solid squad he has to do a lot of experiments, one of them is rebuilding key players for make improve their performance.
Of course, Manchester United must find the right head coach. But also this is not easy for them, because great coaches are really hard to approach at the moment, including Zidane. Maybe Manchester United can try to recruit Xabi, although he doesn't have much experience but at Leverkusen he can form a solid squad, but also Manchester United have to spend more money to recruit him.