The report is highlighted in Diario AS, which claims Madrid offered the highly-rated youngster a new deal but he turned this down in order to secure a move to the English giants.
Born in the Galician city of Ferrol, Fernandez initially starred in the youth levels at Deportivo La Coruna before Madrid beat Barcelona to his signature three years ago.
Fernandez is now aged 17 and has starred in Madrid’s Juvenil C youth team and was tipped to progress through to the professional ranks in the years to come.
The teenager’s contract at Los Blancos expired on 30 June and he has subsequently become a free agent, although such deals often mean his new club may have to pay Madrid a development fee.
Manchester United transfer news has also included a switch for another Spanish full-back, with it widely reported they have agreed a deal with right-back Marc Jurado following his exit from Barcelona.
Image via El Espanol