The Portuguese boss departs after 14 months in charge, with his final game the 1-1 draw at Leeds on Sunday.
Amorim’s dismissal comes after growing tensions between him and the Old Trafford hierarchy, including director of football Jason Wilcox.
It is understood Amorim was dismissed following a Monday morning with Wilcox, United’s director of football, and Omar Berrada, United’s chief executive, in which Amorim was informed he was being relieved of his duties.
In a statement, United confirmed ‘the club’s leadership has reluctantly made the decision that it is the right time to make a change. This will give the team the best opportunity of the highest possible Premier League finish.’
Darren Fletcher will take interim charge, with United next in action at Burnley on Wednesday night.