The forward was substituted by Amorim in the first half of their 2-0 loss to Newcastle United.
Zirkzee was the sacrificial lamb after a terrible opening for the Red Devils, coming off for Kobbie Mainoo.
The supporters booed Zirkzee and cheered his replacement, prompting Gary Neville to say on Sky Sports: “I know that he's earning a lot of money but there's a human being in there that's basically being cheered off by his home fans and that is brutal.”
Head coach Amorim said: “You have to think about the team. The player is suffering during the game. We needed another midfielder. It was tough on me to do that, I talked with Joshua on that. I’m always thinking about the team. At that moment it was important for him to come out.”
“I know that Josh is a really good guy. When he went to the tunnel, I can understand that some guys can be in a bad way but he is a really good lad. It is life, and we will support Josh and continue. Newcastle were better than Manchester United, they weren't better than Josh.”