The Dutchman has often been criticised for his man-management skills during his tenure at the Red Devils, with this revelation shedding a different light on the former Barcelona manager.
Van Gaal is renowned for his brutal and honest attitude when it comes to interviews and discussing his players, though it appears he has a soft and playful side.
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And Mata, who has enjoyed a fine campaign thus far in the Premier League, says he appreciates his manager's honesty and charisma - even if he does go a bit overboard at times.
He said: "I really value his honesty. When someone does something in training that he really likes, he goes over to hug and kiss them – he really does it.
"Or he says in front of everyone: ‘You are the best in training, I’m really proud of how you played,’ to set a good example to others.
"He’s honest and straightforward. He believes in his style of training and way of preparing for games.
"He’s won trophies everywhere he's been and hopefully this season, now we know him better, we’ll win something too."
United will hope such positivity in their training sessions will transfer over to their on-pitch performances following the international break.
The Old Trafford outfit suffered an embarrassing away defeat to Arsenal two weeks ago and need to respond with a win if they're to maintain their title challenge.
The 20-time league champions face Everton at Goodison Park on Saturday in what looks set to be a fierce clash.