Born in Castilleja de Guzmán, Province of Seville, Andalusia, Fernández started playing senior football with Sevilla FC's reserve team at only 17, competing in the Segunda División B.

[2] On 18 December 2013, he made his official debut with the main squad, coming on as a substitute for Piotr Trochowski in a 0–2 home loss against Racing de Santander in the round of 32 of the Copa del Rey.

[3] On 2 March 2014, still before his 18th birthday, Fernández first appeared in La Liga, replacing fellow youth graduate José Antonio Reyes midway through the second half of an eventual 1–0 victory over Real Sociedad also at the Ramón Sánchez Pizjuán Stadium.

[10] On 14 August of the following year, he moved to Granada CF of the top tier also in a temporary deal,[11] scoring ten goals to help them to finish seventh and qualify for the UEFA Europa League for the first time in their history.

[12][13] On 24 January 2021, after being deemed surplus to requirements by manager Julen Lopetegui,[14] Fernández signed a 6+1⁄2-year contract with Real Sociedad, with his former club receiving a transfer fee of a reported €10 million plus another two in variables.