Video footage circulated on social media over the weekend of Mata delaying the departure of United's team bus for training after he recognised nine-year-old Alex Nield in his wheelchair near the players' exit and jogged over to give him a hug and speak to him
Alex's father, Jon Nield, told BBC Radio 5 Live on Monday: "It was just a magical moment. Alex did actually meet Juan Mata after the Norwich game last season.
"We'd called in to Old Trafford to meet a friend and he said 'the players are due shortly to get on the coach', so we hot-footed to the Stretford End.
"Juan had immediately clocked Alex so after he'd gone through the line of people he shot over. A friend of ours, Leon (Labko), captured it all and put it on Facebook and it's just gone absolutely crazy."
Further videos on Labko's Facebook page show Mata's team-mates Matteo Darmian and Ander Herrera also posing for photographs with Alex, who has cerebral palsy.
But it is his reunion with Mata which has struck a chord - particularly after the midfielder arranged an extra treat.
"He even tried to sort him out a ticket because we didn't have one for Sunday's game," said Jon
"We managed to get in to watch the second half - he contacted the club, Juan Mata - so I take my hat off to him.
"It's just a wonderful moment, how he comes over, gives Alex a hug, remembers his name. It was just so touching that a player who everyone sees, (who's so) high-profile, can spend the time to do that for my son, it was brilliant.
"(Alex) is absolutely made up. He probably thinks he's best mates with him, i t's quite surreal really!
"He was so, so happy that he came over, you see the delight on his face as he's chatting to him."
Source: PA