Just four months on from making his first Premier League start, the 18-year-old put in a man-of-the-match performance in Tuesday’s 2-2 draw against Belgium at Wembley.
Mainoo had not even been included in the initial England squad but followed a promising debut off the bench against Brazil by potentially earning a spot at Euro 2024 with his display against Belgium.
That performance has taken the midfielder’s stock to new heights but Ten Hag is confident the success will not go to his head.
“I thought it was very good, but we are not surprised,” the United boss said. “We have seen what he is capable of, that he can very quickly adapt to high levels. It looks very natural.
“We are very happy for him and of course a little bit proud. I would say very proud.
“It’s great for the academy of Manchester United that they bring up a player so young going into the national team. That is a big compliment for the whole club.
“I think definitely in the first place for himself because he did it.
“But also for all the ones who worked with him during his time in the academy, so it’s very good news for Manchester United.”
Asked if he has to manage the hype around Mainoo, Ten Hag said: “Yes, but we have discussed this before and so far he handles it very well.
“If he crosses the line, yeah, of course I as a manager, we as coaches, will interfere.
“But so far it’s not necessary because he enjoys football, he wants to win, he wants to give his best every day because he want to improve.
“As I say, he just wants to have fun on the pitch. For him, it’s fun to play dominant, to dictate the game and to win the game.”
Mainoo was conspicuous by his absence from United’s training photos on Thursday as Ten Hag’s side gear up for the Saturday evening trip to Brentford.
The Red Devils head to the capital looking to kick on after the jaw-dropping 4-3 extra-time win against Liverpool in their FA Cup quarter-final before the international break.
That win gives Manchester United a pep in their step, as does the impending return of centre-back Lisandro Martinez after two months out with a knee injury.
“Yes, there is a chance (Martinez is involved on Saturday),” Ten Hag said.
“We missed him every game because he brings a composure in the team, a calmness in the team.
“And at the same time, a winning attitude and he can express this very clearly, he can transfer this into the team and that contributes a lot to our levels.”
Questions remain over the fitness of Harry Maguire, Casemiro and Jonny Evans, among others, while Amad Diallo joins United’s long-term absentees on the sidelines for the weekend.
Luke Shaw is among those and faces a race against time to make England’s Euro 2024 squad, but Ten Hag expects him back in a United shirt before the end of the campaign.
“Yes, I expect him back before the end of the season,” Ten Hag said. “That is the plan and he’s still on schedule on this. He will return to our team.”
