Manchester United have signed Real Madrid youngster Alvaro Fernandez on a four-year contract, sources have confirmed to ESPN.

The 17-year-old left-back -- whose deal at the Bernabeu expired on June 30 after a failure to reach an agreement on a renewal -- moves to Old Trafford as a free agent.

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Fernandez joined Real Madrid from Deportivo La Coruna in his native Galicia in 2017, beating competition from a number of top clubs for his signature.

The defender played for Madrid's Under-15s, U16s and U17s in his three seasons at Valdebebas, being known as an attacking full-back with impressive physique and pace.

He was part of a talented generation that features some of the most highly-rated players in Real Madrid's academy such as midfielder Bruno Iglesias and forward Israel Salazar.

Sources have told ESPN that Fernandez views United as a better option for his development in the short and medium-term.

He is expected to feature for United's reserves next season, with the possibility of training with the first team when defensive reinforcements are required -- a faster career progression than would have been available in Madrid.

The signing of Fernandez is not the first time that Manchester United have targeted the academies of La Liga clubs this summer.

Last month ESPN reported that Barcelona right-back Marc Jurado, 16, will also move to Old Trafford, despite being offered a new three-year deal at Camp Nou.

ESPN's Alex Kirkland contributed to this report.