The 21-year-old midfielder, speaking to reporters at England's pre-tournament training camp in Florida, was honest about the toll that Amorim's decision to exclude him took across the first half of the season — during which he failed to start a single Premier League match and accumulated barely 183 minutes of league football before Amorim was dismissed on January 5.
"Obviously there were difficult times," Mainoo said. "But I tried to keep my focus on what was in front of me, take things day by day and just keep working my craft, keep working hard for the team, and I hoped the rest would come. Thankfully it has."
He was equally candid when asked whether Carrick deserved credit for his World Cup selection.
"Definitely, and I told him that I was very grateful. Because if he hadn't put me on the pitch, then I wouldn't have been here, so I'm always grateful to him for that."
Mainoo started all 16 available matches under Carrick after the manager's appointment in January, playing the full 90 minutes on 15 occasions as United finished third in the Premier League. The transformation was so complete that Manchester United rewarded him with a new five-year contract.
Mainoo is now one of the most talked-about names in England's midfield ahead of the tournament and was bullish about the team's chances.
"One hundred per cent we can win it. I feel like everyone in the squad, staff, everyone believes we can win it. It's very special, something I've dreamed of. So to be here and say that I'm playing in a World Cup is unbelievable."