Amorim's 14-month tenure came to an end on Monday morning after a 1-1 draw against Leeds United left the Red Devils in 6th place.
The Portuguese tactician departed with a £10M pay-off, followed by his coaching staff, who have been replaced before the announcement of the club’s caretaker manager that should come over the next month.
Mainoo, who has often been in conflict with Amorim is yet to start a Premier League game this season and has been desperate for a move away from the club.
The England star caught the attention of fans this week as he followed in the footsteps of former United star Alejandro Gernacho in reacting to Amorim’s sacking.
While Garnacho liked a post from Fabrizio Romano announcing Amorim’s sacking, Mainoo has gone one step further and liked a post stating:
"I'd be laughing too after getting a £10mil payout” with the main text reading “Amorim after hiring all his best mates to be coaching staff and getting them a fat payout.”
His dismissal means that United spent a staggering £27m to hire and then fire Amorim which, as the club made mass redundancies last year, is not a good look.
Mainoo’s future is unclear as the January transfer window continues, interest is still high from Serie A sides but as the club looks for a new manager it seems likely that he will leave in the summer instead.