According to France Football (h/t Tom Coast of Sport Witness), the Red Devils do not have an option to extend his current deal and Mata wants a return to Spain. Former club Valencia would be the dream destination.
Daniel Cutts of The Sun reported on the possibility of a return to Los Che in the summer. According to the Daily Star's Harry Pratt Arsenal are also now interested in the Spaniard due to the connection to former coach Unai Emery.
Mata played for Valencia between 2007 and 2011 before making the switch to England. He joined Chelsea and moved to Old Trafford in 2014, continuing his excellent play as a wide man and attacking midfielder.
The 30-year-old has started five Premier League matches so far this season and isn't seen as a long-term priority for United. There has been little talk about a possible contract extension, even though time is running out should that be the direction United want to go.
Mata would be free to open talks with foreign clubs in January should the current situation hold, agreeing to a possible pre-contract and joining a team like Valencia on a free transfer in the summer.
Los Che have tried their best to hunt for bargains in recent years due to the unstable financial situation of the club.
Their financial struggles have seen the club's stature fall in the last few seasons, and while they did manage to secure UEFA Champions League qualification during the 2017-18 campaign, the new season has once again turned sour.
Los Che sit in 15th place in La Liga and chase Juventus and United in their Champions League group, with an early exit from Europe's top club competition looking likely.
A move for Mata on a free transfer would be an excellent bit of business for Valencia, as they need all the help they can get and would love the positive publicity that would come with the return of a club hero.