Garner, 19, has made seven first-team appearances for United - having spent 11 years in the club's youth ranks - but only appeared once in the Premier League.
This season the midfielder is out on loan at Championship side Watford, for whom he has made 10 appearances thus far.
“I've played with some top, top players, but I have to say Juan Mata is class," stated Garner.
“Everything about him – his touch, his pass, how he speaks to you on and off the pitch – he's just a real nice guy."
Now Mata has responded to Garner's comments with some words of his own, hailing the “cleverness" of the youngster.
“He is a good friend, that's why he speaks so well of me!" the Spaniard told The United Review.
“I always thought he is one of the players who, if he keeps going and keeps improving, in the way he was doing in the Academy, he can be a very, very good midfielder.
“I really like him; the way he plays on the ball, his cleverness, his way of looking forward, looking for a pass and also his attitude off the ball. So, whenever he was here, I always tried to encourage him and said what I believed he could be as a player.
“I always tried to motivate him and give him confidence as I think, when you're that age, you need confidence and trust - not only from the manager but also from your team-mates.
“I wish him all the best at Watford and I am sure he will do well. He's a great guy and a very good player, as I've said before, because he keeps improving every day.“