Speaking to Sky Sports, the 21-year-old academy product — who scored an FA Cup final winner against Manchester City in 2024 and played at the European Championship within a year of his debut — reflected on a painful period in which he was not given a single Premier League start by Amorim.
"When there's new managers, they have their way that they want to play and if they think you don't fit that, then you don't fit that. Going from playing nearly every game to not playing as often is always going to be a difficult adjustment. It was good for me in terms of learning about myself, the game, and patience."
"It's difficult when you don't even come on as a sub of course. But I'd say my family and my friends helped me see the light at the end of the tunnel. They knew it would swing back my way at some point, so I just had to be patient."
He confirmed the doubts were real, and that a departure was considered.
"When you're not playing many games, or any games, you consider all things. But at the forefront of my mind was always to play for Manchester United and continue to play for this club that I've grown up at."
Mainoo had submitted a loan request in August which was rejected, and by January his name was being linked with Napoli. He leaned on Casemiro, Bruno Fernandes and close friend Joshua Zirkzee during the lowest moments.
Carrick arrived in January and immediately restored Mainoo to the central midfield role he had thrived in under Erik ten Hag. He has since started 12 of his manager's 13 Premier League games, scored the winner in the 3-2 victory over Liverpool at Old Trafford, signed a new contract and been recalled by England head coach Thomas Tuchel.
His description of what makes Carrick different was direct.
"Just talking to you like a person — it's not just business. That definitely helps as a player when a coach can see the other side of the game, which obviously he can because he's been there and been in that position. You can believe everything that he says because he's been there and he's played for this club. He knows what comes on the football pitch, he knows what happens off it. Everything he says is a gem, really."
Amorim, in Mainoo's final months under him, publicly defended his selection calls.
"I understand what you are saying. You love Kobbie, he starts for England. But that doesn't mean that I need to put Kobbie in when I feel that I shouldn't put Kobbie in, so it's my decision."
Mainoo made 212 Premier League minutes under Amorim across the first half of the season. He has played over 1,000 since Carrick arrived.