Manchester United forwards Marcus Rashford and Alejandro Garnacho were left at home for Sunday’s Manchester derby.
Amorim told Sky Sports that he evaluated “training, performance, game performance, engagement with the teammates, (and) pushing the teammates up” before deciding to exclude them from the matchday squad.
Amorim also handed starts to Harry Maguire and Mason Mount while dropping Casemiro to the bench.
“I don’t want to send a message. It’s simply an evaluation, and they know it,” Amorim said. “The players are really, really smart. Everybody understands my decision. I have to choose. It’s just simple selection.
“The context is difficult. We have to win games and we have a difficult situation. I pay attention to everything, the way you eat, the way you put on your clothes to go the game. Everything. I make my evaluation and then I have to decide. I have a lot of players to choose.”
Manchester United went on to claim a stunning 2-1 win at the Etihad Stadium, scoring two quick goals in the closing minutes to come from behind and hand Pep Guardiola’s side another defeat.