Reports earlier in the year suggested that United had already activated a one-year option to extend his contract. But sources have confirmed this is not the case.
And Valencia are planning to capitalise on the uncertainty over Mata's situation.
At the same time, the Old Trafford club would be keen to remove Mata's £170k-a-week from the wage bill.
The Spaniard would be happy to stay in Manchester, where he recently opened a restaurant with his father.