On 29 June 2010, after being promoted to the reserves in the Segunda División B, Fernández was called up to the first team for the preseason as a backup to Gorka Iraizoz and Raúl Fernández.[1] However, he only appeared in 19 matches for the former during the season, mainly due to a hand injury which kept him out for two months,[2][3] and struggled even more in 2011–12 again due to injuries, being overtaken by new signing Jon Ander Serantes.[4][5]
Fernández was loaned to Barakaldo CF of the same league on 22 July 2012 for one year,[6] but had his contract with the Lions terminated on 28 January 2013.[7] He signed a two-and-a-half-year deal with Villarreal CF a day later, being assigned to the B side also in the third tier.[8]
Numancia
On 6 July 2016, Fernández signed for Segunda División club CD Numancia on a two-year contract.[9] He made his professional debut on 4 September 2016, starting in a 1–1 away draw against AD Alcorcón.[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.[11] On 27 February 2017, he extended his link until 2020.[12]
Levante
Fernández agreed to a four-year contract with La Liga side Levante UD on 23 July 2018.[13] His maiden appearance in the competition took place on 2 February 2019, in a 0–0 home draw with Getafe CF.[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.[16] He signed a new deal until 2023 the same month,[17] the new buyout clause being set at €30 million.[18]
Osasuna
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]
International career
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.[20][21]
^Hernández Casado, Luis (12 June 2018). "Aitor, un portero que suma puntos" [Aitor, a goalkeeper who keeps adding points]. Heraldo de Soria (in Spanish). Retrieved 17 August 2018.
^López Sanfeliu, Álex (13 November 2019). "Aitor Fernández renueva al alza con el Levante" [Aitor Fernández renews on the rise with Levante] (in Spanish). El Desmarque. Retrieved 17 November 2019.