Carrick’s arrival signalled a new dawn for Mainoo, 21, at Man United, bringing the midfielder back into the fold after being outcast by Ruben Amorim.
It had gotten so bad for the academy product that he even considered leaving his boyhood club over the lack of minutes.
Mainoo has since played the full 90 minutes in 14 of his 16 games under Carrick and earned a place in Thomas Tuchel’s England squad for the 2026 World Cup.
Despite his international recall, Mainoo didn’t play a single minute at the tournament, though it felt like England were crying out for a player with his ball-carrying abilities at times.
"I spoke to him all the way through the World Cup, not loads, but little bits," Carrick told BBC Sport.
"It's challenging. From the outside we all see the glitz, the glamour and all the positive sides of football.
"But players are human beings. We all have our ups and downs. It's important we support each other.
"It was a good experience for Kobbie. It's a World Cup and that is a big step.
"He's still such a young man and he's achieved so much, so quickly. To be at the stage he's at is an achievement."