The Eagles have exercised the option to purchase the player on a permanent basis after he spent the second half of the season on loan at Estadio da Luz.
Fernandez made 16 appearances and scored once for Benfica during his loan spell, as Roger Schmidt's side finished second in the Primeira Liga table, behind Sporting Club, of Lisbon.
The 21-year-old also ran out for Granada during the 2023/24 campaign, playing 14 times for the La Liga outfit, who had Facundo Pellistri on their books from January onwards.