The England international was frozen out of the starting XI by former manager Ruben Amorim before being brought back into the fold by Carrick in the second half of the 2025/26 season.
As United sealed UEFA Champions League qualification, Carrick agreed a deal to take charge permanently at Old Trafford, and the former England international has spent heavily on new faces this summer.
Midfield has been a key focus, with transfer deals to land Youri Tielemans, Carlos Baleba and Andrey Santos, which had looked to potentially reset Mainoo's revived progress.
The 21-year-old has featured in both of United's Premier League games so far in 2026/27 and Carrick is counting on him for the months ahead.
"Kobbie Mainoo can have another big season. He has come back great, and you can see him growing in personality and maturity.
“He is still so young, and there's loads to still come from him, which is great."