Manchester United boss Erik ten Hag was delighted with Kobbie Mainoo for victory over Arsenal in New Jersey.
Mainoo laid on the opener struck by captain Bruno Fernandes for the 2-0 win.
Ten Hag said: "It's fantastic. Manchester United is famous for always bringing young players up and it can be done. But we have to see.
"We have confidence, he [Kobbie Mainoo] is playing with confidence, and I really like his performance. But this year, he showed it in spring, then he got injured. We are really happy. There are more youngsters with us now and they're all doing very good. But I don't want to rise expectations too high.
"We have to see. The Premier League is tough but, definitely, you can see we have some really good young players who can play a role in the squad. But the bar is high."