Born in Arrasate, Gipuzkoa, Basque Country, Fernández joined Athletic Bilbao's youth setup in 2003, aged 12.

[10] Initially a backup to Munir, Fernández profited from national call-ups and became a regular starter, holding that position until the end of the campaign.

[14] In November 2019, it was announced that Fernández might miss Levante's next match as he had been called by his local town to work at a polling station for the Spanish general election,[15] however he was later excused from this.

[18] On 2 July 2022, after Levante's relegation, Fernández remained in the top flight on a three-year deal at CA Osasuna, with a release clause of €14 million.

[19] Fernández made his debut for the unofficial Basque Country national team on 30 May 2019, in a 0–0 draw away to Panama for which a small, youthful and inexperienced squad was selected.