Mainoo, 20, has been in discussions with the club over a deal expected to run until 2031 — a five-year extension that would come with a significant salary increase on the contract he signed in 2023, when he was just 17 and breaking into the first team.
Carrick was measured but positive when asked directly about the situation.
"It's getting closer, so we're positive with that."
He gave no indication of concern about the outcome.
"Time will tell how it goes but we are calm with it and at the moment, we are in a good place."
The news represents a remarkable turnaround. At the turn of the year, Mainoo's future at Old Trafford appeared all but over. Under Ruben Amorim, he did not start a single Premier League match all season, and a loan move to Napoli was being seriously discussed. His situation looked bleak.
Then Carrick arrived. Since taking charge in January, the interim boss has started Mainoo in all ten of his Premier League games. The midfielder has been central to a run of seven wins in those ten matches, helping United climb to third and into genuine Champions League contention.
The England recall followed — his first in 18 months — and the contract discussions, which had been dormant, gathered pace. Harry Maguire signed his extension last week. Mainoo appears set to be next.
Carrick also underlined why securing Champions League football matters beyond results on the pitch.
"The Champions League just brings so many positive things. It's where we want to be. That has ramifications for players staying, players coming in, financially."
A few months ago it was unimaginable that Mainoo would still be a Manchester United player next season. Now he looks set to be the foundation of their next chapter.