The Spaniard was one of the few positives out of the uninspiring match, scoring a brace against the foxes to help put United in the lead.
The Red Devils had conceded in the first half from a well worked Jamie Vardy effort and the clash started to look as though it would not go in their favour.
However, Mata came to the rescue with a neat finish and a sublime free-kick to complete United’s comeback; or so fans though.
Harry Maguire would grab a last gasp goal to equalise for Leicester and destroy the away fans hopes of keeping up with Manchester City but Neville was impressed with Juan’s performance.
Speaking to Sky Sports, Gary said: “He’s composed in all areas of the pitch but [especially] in front of goal. He’s high quality.
“He had a good game. He was a big influence and made two really, really good finishes.”
The Portuguese manager let the Spaniard go after dropping him to the bench and deeming him surplus to requirements.
United fans were pleased to get their hands on a proven player and Mata quickly settled into matters at Old Trafford.
The tricky playmaker was consistently impressive and hardly put a foot wrong but Mourinho’s move to the Red Devils suddenly saw his starting XI spot at risk.
Many predicted that the pragmatic manager would sell Juan at the earliest opportunity but Jose stuck to his early promise of keeping the Spaniard and after the player’s brace vs Leicester, must be thankful that he did.