Manchester United star Mata has emerged as a key player for Mourinho in recent times, helping the 55-year-old lift the doom and gloom mood around Old Trafford.
The Spain international struck a stunning free-kick against Newcastle at the start of October as the Red Devils rallied from 2-0 down to take all three points.
And Mata was again the hero for Manchester United on Wednesday, scoring another sublime set-piece to help them rock Juventus 2-1 at the Allianz Stadium in the Champions League.
New details about their relationship have, however, come to light since.
The Daily Mail claim Mata was unhappy with Mourinho after the club’s Carabao Cup exit to Derby at the end of September.
United were 1-0 up in that match before a sublime free-kick from Harry Wilson.
But Sergio Romero then saw red, forcing Mourinho to alter his tactics.
Mata ended up being the fall guy, with the United boss withdrawing him for goalkeeper Lee Grant.
And the Daily Mail claim Mata was unhappy with the decision, though still wants to stay at the club.
The player is yet to sign a contract extension with his current deal expiring at the end of the season.
Arsenal and Valencia have both emerged as potential destinations for the Spain international.
Meanwhile, Mata has opened up on his heroics against Juventus, revealing what he told Ashley Young before curling home the free-kick.
“As soon as there was the free-kick in there, I had the confidence that I had to take it,” he told the club’s official website.
“I told Ash: ‘Please let me take it, because I can go over the wall.’
“It’s very difficult for the goalkeeper because they don’t see a lot with the wall so close.
“So I tried to do what I do in training a lot of times, practicing, practicing.
“It was important to score to make it 1-1 and, after, it led us to the 1-2.
“I think because of the venue and the importance of the game, it’s one of the best [that I’ve scored].”