Football Express News understands Valencia defender Nicolas Otamendi has handed in a transfer request.
Valencia do not want to sell their impressive central defender, but interest from Man United and Real Madrid has caused concern amongst Mestalla officials.
English side United are keen to sign a new centre back this summer after relying heavily in the likes of Tyler Blackett and Paddy McNair.
27-year-old Otamendi joined Valencia from Porto last summer and has been one of the standout centre-backs in La Liga.
A number of reports in Spain have claimed a deal has been agreed between the player and United, pending a transfer fee agreement but confirmation of those talks are yet to be heard or seen.
And, fueling more transfer gossip, it is now understood that the Argentine international has handed in an official transfer request.
Otamendi is contracted to Valencia until 2019.