Mata has started 15 Premier League games this season. Getty

Manchester United have five months to make a decision over Juan Mata's future at Old Trafford even though the Spaniard's current contract is due to expire at the end of the season.

Players out of contract at the end of the campaign are free to negotiate a move away to another European club from 1 January.

However, Spanish publication AS says that United will still have the final word on Mata's future due to a clause inserted in his contract when the Spaniard was brought from Chelsea in January 2014.

Mata then sign a four-and-a-half year deal but United included an option to extend it by another 12 months.

The Premier League giants are yet to make a decision but AS report that Jose Mourinho's side still have until the end of May to trigger that option which will automatically keep the former Valencia star until June 2019.

Mata's future at United came under question in the summer of 2016 after Mourinho took over from Louis van Gaal.

The 29-year-old playmaker left Stamford Bridge after falling out of favour with the Portuguese tactician, despite having been named Chelsea's player of the season in 2011-12 and 2012-13.

However, Mata has played an important role under Mourinho.

The Spaniard helped United win the Europa League and the League Cup during Mourinho's first season in charge and has already made 22 appearances during the opening half of the current campaign, scoring three goals and providing three assists.

In October, The Mirror reported that Mata had turned down a big-money move to the Chinese Super League to stay at United.

The report said that Mata could have earned much more than his current £165,000-a-week salary but he opted to remain and United were set to trigger the option to keep him one more campaign.

Mata himself admitted a month later he would like to sign a new deal at United after claiming that he would like to follow in the footsteps of Ryan Giggs and play for the Red Devils into his 40s.

"Why not? I'm 29 and hopefully I can play football for some years, Mata told ESPN FC. "It would be great to play until I'm 40 like Ryan Giggs. But that's still a bit far - still 11 years. "You never know what can happen in football and in life. But my feeling now is that I'm happy here and I wouldn't have any problem continuing here for more time."

However, AS point out that United are yet to inform Mata about their long-term plans and the Spaniard will thus be free to negotiate a move to a rival club if the Premier League giants do not make a decision before May.