Neither Garnacho nor fellow attacker Rashford were named in the matchday ranks for the clash with the champions at the Etihad, a decision that surprised both fans and pundits alike.
Instead, Mason Mount and Amad Diallo were selected to play behind Rasmus Hojlund as Amorim's two number 10s, with Bruno Fernandes seemingly dropping deeper to partner Manuel Ugarte in midfield.
Antony and Joshua Zirkzee represent the only out-and-out attacking options on the Man United bench, and Amorim was inevitably quizzed on his bold selection call, which comes at a time when Rashford and Garnacho are both being linked with moves away.
Speaking to Sky Sports News, the Portuguese simply stated that it was a "selection" decision, and both Rashford and Garnacho are "alright" despite the brutal snub from the manager.
Amorim details reason for Rashford, Garnacho snubs
"Selection," Amorim said when asked why Rashford and Garnacho were dropped. "We try to evaluate everything: training, performance, game performance, engagement with the team-mates, pushing the team-mates up. Everything is on the line when we analyse and try to choose the players, so that is my selection. Simple.
"I don't want to send a message. It's simply an evaluation, and they know it. 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."
Asked how Rashford and Garnacho found out they would not be involved in the derby, Amorim replied: "It's the same all the time. There's a communication after the last training which goes to the WhatsApp. They receive the information. But they are alright. They had training this morning. I was there. Everything was OK. They trained really well."
Man United travelled to the Etihad eight points and eight places below Manchester City in the Premier League table, and defeat at the Etihad would see Amorim lose three straight league matches for the first time in his managerial career.
Could the end be near for Rashford and Garnacho?
The arrival of Amorim had ostensibly triggered an upturn in fortunes for Rashford, who scored three goals in his first two Premier League games under the Portuguese but did not make the starting lineup for either loss to Arsenal or Nottingham Forest.
The Englishman also lasted just under an hour in Thursday's Europa League triumph over Viktoria Plzen, and while we may never know whether any off-field misdemeanours or disagreements led to his demotion, it is nothing new.
When Erik ten Hag was in charge, Rashford was dropped from the starting lineup once for being late to a team meeting in late 2022, before the infamous trip to Dublin and subsequent sanction earlier this year.
The case of Garnacho may be a more surprising one at face value, but the Argentine did not get to the 60-minute mark against Arsenal or Forest, and an out-of-sorts Antony being selected for the bench ahead of him does speak volumes.
Only eight or nine players are though to have been deemed unsellable by the Man United hierarchy, but neither Garnacho nor Rashford are thought to be among the indispensable pack, and Sunday's snubs suggest that January departures for both are not beyond the realm of possibility.
Written by
Ben Knapton