Yes exactly the same as the Morata situation. He went to Juventus for a couple of seasons, did well enough that rumours started to circulate that teams like United, Liverpool, Chelsea, Arsenal, City etc might try & go for him.
Real had a buy back clause, bought him back for I think it was £30m after selling him for £20m 2 seasons prior. They kept him for 1 season in which he did again decently enough & then sold him on to Chelsea for £60m.
Only way I'd be content with a buy back clause would be if it was an extravagant buy back fee ie we buy him for £20m, if they want him back at any point it's £70m.. that I would be somewhat OK with. Otherwise I wouldn't even entertain it, for a club as big as Manchester United, even in our decline in recent years, accepting such a clause would be an insult IMO.