|Full name||Jon Gaztañaga Arrospide|
|Date of birth||28 June 1991|
|Place of birth||Andoain, Spain|
|Height||1.82 m (6 ft 0 in)|
|Playing position||Centre back / Defensive midfielder|
|2009–2014||Real Sociedad B||115||(3)|
|2015||→ Ponferradina (loan)||12||(0)|
|2015–2016||→ Numancia (loan)||34||(0)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 23:23, 7 October 2018 (UTC)|
Born in Andoain, Gipuzkoa, Gaztañaga was a product of Real Sociedad's youth system. He made his senior debuts with the B-team, spending several seasons in Segunda División B with the side and also achieving promotion from Tercera División in 2010.
On 18 August 2013, Gaztañaga made his official debut with the main squad, replacing fellow youth graduate Gorka Elustondo in the dying minutes of the 2–0 La Liga home win against Getafe CF. His first appearance in the UEFA Champions League took place on 10 December, as he came on for Mikel González in a 0–1 group stage home defeat to Bayer 04 Leverkusen.
In early 2014, Gaztañaga renewed his contract with Real Sociedad until 2016, being definitely promoted to the first team in May. On 26 January 2015, after appearing sparingly during the first half of the campaign, he joined Segunda División club SD Ponferradina on loan until June.
On 9 July 2015, Gaztañaga was loaned to fellow league team CD Numancia for one year. On 22 August 2017, he agreed to a three-year deal with Gimnàstic de Tarragona also from the second level after cutting ties with Sanse.
On 13 June 2018, Gaztañaga terminated his contract with Nàstic. On 20 August, he moved abroad for the first time in his career and joined Cypriot First Division club AEL Limassol. Five days later, he made his debut, coming on as a substitute for Marko Adamović in a 1–0 league victory against Ermis Aradippou FC.
- "Sociedad start with a win". ESPN FC. 18 August 2013. Retrieved 20 August 2013.
- "Toprak fires Leverkusen through". ESPN FC. 10 December 2013. Retrieved 10 December 2013.
- Gaztañaga y Berchiche renuevan con la Real Sociedad hasta 2016 (Gaztañaga and Berchiche renew with Real Sociedad until 2016); Real Sociedad, 8 January 2014 (in Spanish)
- El sueño de Joseba y Jon (Joseba and Jon's dream); Real Sociedad, 20 May 2014 (in Spanish)
- Jon Gaztañaga, S.D. Ponferradinara utzita (Jon Gaztañaga, loaned to S.D. Ponferradina), Real Sociedad, 26 January 2015 (in Basque)
- Jon Gaztañaga joins C.D. Numancia on loan; Real Sociedad, 9 July 2015
- Jon Gaztañaga, nou jugador grana (Jon Gaztañaga, new grana player); Gimnàstic Tarragona, 22 August 2017 (in Catalan)
- Matilla, Gaztañaga i Perales finalitzen la seva etapa a Tarragona (Matilla, Gaztañaga and Perales end their spells in Tarragona); Gimnàstic Tarragona, 13 June 2018 (in Catalan)
- "Gaztañaga firma con el AEL Limassol" [Gaztañaga signs with the AEL Limassol] (in Spanish). ElDes Marque. 20 August 2018. Retrieved 28 September 2018.
- "Gaztañaga debuta con victoria en el AEL Limassol" [Gaztañaga debuts with victory in AEL Limassol] (in Spanish). El Diario Vasco. 25 August 2018. Retrieved 28 September 2018.
- "Stupendous Spain win U17 crown". UEFA. 16 May 2008. Archived from the original on 30 June 2012. Retrieved 20 August 2013.
- XXXV Torneo Internacional Sub.-18 (XXXV Under-18 International Tournament); Royal Spanish Football Federation, 30 January 2009 (in Spanish)
- España revalida su condición de campeón en el Torneo Atlántico, tras derrotar a Alemania, 4–1. (Spain win Atlantic Tournament again, after beating Germany 4–1.); Royal Spanish Football Federation, 6 February 2009 (in Spanish)