Zaldúa appeared in his first official match with the main squad on 23 November 2013, featuring the first 80 minutes before being substituted for Javi Ros in a 4–3 La Liga home win against RC Celta de Vigo.[2] Roughly a month later, he signed a new deal with the Basques until 2016.[3]
On 20 May 2014, Zaldúa renewed his contract with the Txuri-urdin until 2018, and was definitely promoted to the first team.[4] On 4 July 2017, he was loaned to fellow top-flight club CD Leganés for one year.[5] He made 30 appearances as the side from the outskirts of Madrid avoided relegation, and scored a last-minute equaliser in a 2–2 draw at Deportivo Alavés on 21 January 2018.[6] On 7 May, he was sent off in a 3–0 home loss to Levante UD for denying José Luis Morales a goalscoring opportunity.[7]
Zaldúa scored his only goal for Real Sociedad on 12 May 2019 in a 3–1 victory over Real Madrid at Anoeta Stadium, but was replaced in the same game with a broken left leg.[8] He totalled 190 matches during his spell.[9]
Cádiz
On 11 July 2022, Zaldúa joined Cádiz CF on a three-year contract.[10] He spent the vast majority of his first season on the sidelines, nursing a serious knee injury.[11]
^Lorenzo, José Luis (10 July 2022). "Joseba Zaldua, 16 años en blanco y azul" [Joseba Zaldua, 16 years in white-and-blue]. Noticias de Gipuzkoa (in Spanish). Retrieved 12 May 2024.