Tuanzebe, 22, has not played for United's senior side for almost a year due to a run of frustrating injuries, but was a starter against the likes of Kylian Mbappe and Neymar in Paris on Tuesday night.
Hargreaves said: "Good luck getting this guy out of the team... I love him! He wasn't fazed by Mbappe or the occasion... this young man is not getting out of the side."
Ferdinand agreed, saying: "He was smelling danger... he snuffed out danger many a time today, you have to reward performances like that... he deserved to be rewarded."
Fletcher added: "He didn't even look like he was panicked or running full pelt; he looked like 'Oh right, it's Mbappe' - he was comfortable and he just dealt with it. Top class."