The Red Devils opened their pre-season campaign with a 2-0 win over Wigan Athletic on Saturday afternoon courtesy of second-half goals from substitutes Will Keane and Andreas Pereira.
Tuanzebe, 18, was introduced in the 80th minute of the friendly and Mourinho has talked up the qualities of the centre-back, who is now pushing for a spot in the squad that will travel to China later this month.
"You can play 90 minutes or one minute, sometimes one minute is enough," Mourinho told MUTV. "With Axel, 10 minutes is enough. I only needed 10 minutes to know his potential, you can see it immediately."