United drew 1-1 in their opening pre-season clash in Arizona, and Mourinho was impressed with Chong's contribution, per MUTV (h/t Sky Sports):
"He was good. He came with the intention to show, and in a moment where we have no strikers on the pitch, Martial was the only one and then he left, so we needed people to create, have some initiative, which he did. The action for the cross for the goal is a beautiful action. He was enthusiastic, he was confident to play.
"Of course physically he has his limitations, and when he has one more touch and he allows that body contact of course he loses it, but when he makes the ball move and attacks people one against one, he has quality. He's a good kid."
Chong has impressed at youth level for United in the last two seasons since moving to the club from Feyenoord.
The Dutchman's senior debut in the United States will have prompted plenty of excitement among Red Devils fans.
Per football analyst David O'Brien, he could eventually be the answer to United's longstanding issues on the right flank:
Mourinho has an abundance of talented attacking players in his front line, but none are naturally right-sided.
Alexis Sanchez, Anthony Martial and Marcus Rashford all prefer to play on the left, while Jesse Lingard and Mata are better-suited to the No. 10 role.
Chong can play on either flank, but his preference is for the right wing, and his impressive dribbling and directness make him a dangerous player.
As Mourinho noted, his game still has some way to go before he can become a first-team regular. But Chong's showing against Club America will have given him plenty of confidence.