Five-time Champions League winner Casemiro has returned to the United starting XI after missing much of this season with injury, and has looked impressive beside exciting youngster Mainoo in central midfield.
"Casemiro is a very important player for our game, so we are happy he's back and Kobbie Mainoo can learn a lot from that togetherness," said Ten Hag.
"Kobbie is very coachable and Casemiro has so much experience and that can even accelerate his development. When they play together, I think they can benefit each other.
"Casemiro has taken to him [Mainoo]. He's talking to him. I see it in the dressing room. I see it on the pitch.
"In the training, also in games. Of course he's looking at his own game, but he's trying to help and to support."
Eighteen-year-old Mainoo has recovered from his own injury issues suffered in pre-season to force his way into Ten Hag's team, scoring his first goal in the FA Cup win at Newport and his second shortly after in the dramatic win at Wolves.
"I had that confidence because I saw him performing," added the Dutch manager. "I saw him performing in autumn. I saw him progressing during spring and in summer, I had the game from Arsenal in my mind so I didn't have any doubt.
"We are now building a team. What it can really offer is foundation for players to come in. We built a foundation that we really can add quality [to] and place into the squad to bring the team to the next level."