The decision followed a tense press conference on Sunday, where Amorim expressed frustration with the club's hierarchy and transfer strategy after a 1-1 draw with Leeds.
Amorim had previously hinted at discontent behind the scenes and avoided clarifying his recent remarks about the club's transfer plans.
Pundit Gary Neville suggested Amorim was 'starting to unleash' due to unhappiness, drawing parallels with Enzo Maresca's departure from Chelsea.
Neville speculated that Amorim's frustration likely stemmed from a lack of further investment in players, despite Manchester United spending over £200m last summer.