I think the main problem with this United team had its foundation laid out in the last years of Fergie. During its glory years under Fergie, United always featured great players from their youth academy on their team. With their youth academy constantly producing good talent and almost all of their young player investments working out (Cristiano Ronaldo, Wayne Rooney etc.) they didn't really care for spending money on "ready to go" players and splash in the market. In the last couple of years, the youth academy players of United have been utter garbage. Tom Cleverley, Chris Smalling, Jonny Evans...These guys are not on United level. Hell, they're not even on Southampton level. As a result, they rather panicked and spent money on players who are just not worth their price. (Maroune Fellaini, Ashley Young)
I expect a complete transition in team management department for the team. They're likely to rely upon their ability to spend money for a couple of years. Looks like they've already started it, really.