The England striker revealed that he didn't enjoy Mourinho's rigid tactical approach and prefers when he is given the chance to roam freely across the pitch.
Speaking with former United stars Rio Ferdinand and Wayne Rooney on the BT Sport show 'Between the Lines', Rashford said of interchanging positions: "I think that's when we play our best football.
"I think under Jose, it was a bit like 'you play there, you play there and you play there.'
"You can do a job but it is difficult for me to play my best football."
Rooney also reflected on his United career under the club's legendary former manager Sir Alex Ferguson and believes switching positions was a key reason for his success at Old Trafford.
He said: "I always quite good at reading the game and it does take a long time to be able to do that.
"I always felt if I was struggling in a game if that was out wide, a striker or in a no.10 position, I'd always try and occupy a different position which is causing the opposition the problems.
"But what we had was good rotation. We had Tevez, Ronaldo, Louis Saha, Park Ji-sung, great players. We interchanged our positions a lot and caused problems for teams.
"I think it's good we had that freedom."