Carrick was speaking at his pre-match press conference before the final day of the season, with Manchester United already confirmed in third place and heading into next season in the Champions League.
Casemiro played his final game for the club last weekend before departing as a free agent, and Manuel Ugarte is also expected to leave. United have signalled clearly that replacing both players is the priority this summer.
The names on the midfield shortlist are substantial. Sandro Tonali of Newcastle United has been identified as Carrick's primary target, with Gianluca Di Marzio reporting concrete United interest. Ederson of Atalanta is also understood to be close to an agreement. Nottingham Forest's Elliot Anderson, Carlos Baleba and Adam Wharton have all been credited with interest in recent weeks.
When asked specifically about finding the right partner for Mainoo, Carrick was careful not to reduce the recruitment process to a single relationship.
"There's a balance as a football club, because you're not necessarily bringing a player in just to play with one player. It's about fitting the squad, the balance of the squad, being able to cope with playing in different competitions for so many games."
He made clear, however, that Mainoo's qualities make the search more straightforward than it might otherwise be.
"The beauty about Kobbie is that he can do so many things well. I think he's proven that, and he's evolved so much in the four or five months that I've seen his progress. That's him — I'm not taking credit for that. He's done that himself. He can do so many things, so it makes bringing players in to play with a player like Kobbie a little bit easier when he can adapt himself."
Mainoo, 21, signed a new five-year contract last month keeping him at Old Trafford until 2031. He had been frozen out under Ruben Amorim and came close to leaving in January, but has started all but one of United's league matches since Carrick took over — missing only through injury. His wages were reported to have quadrupled to around £120,000 per week under the new deal.
United won 11 of 16 matches under Carrick this season. Mainoo started every one where he was fit.