La Razon says Mata could be on the verge of a return to Valencia.
Owner Peter Lim has welcomed the signing of the former Spanish international, who is out of contract at the end of the season.
Lim is happy to sign Mata because Valencia will not have to pay a transfer fee.
The 32-year-old has struggled to hold down a place at United in recent years, making just 19 Premier League appearances last season.
Valencia reportedly gave their players IOU notes in August 2020 because they could not afford to pay them. They are also at risk of being relegated from LaLiga for the first time since 1986.