On 19 June 2013, Eraso was released by the Lions and joined Leganés also of the third division the following month. He appeared in 42 games during the campaign, as the Madrid club was promoted to Segunda División after a ten-year absence.
Eraso played his first match as a professional on 7 September 2014, starting in a 3–1 home win against Mallorca. He scored his first goal in the second tier on 21 December, the last in 2–0 home victory over Recreativo de Huelva.
On 31 May 2015, Eraso scored a hat-trick in a 5–2 away rout of Barcelona B. He returned to Athletic on 1 July, now being assigned to the first team in La Liga.
Eraso made his official debut for Athletic on 30 July 2015, starting and scoring both goals in a 2–0 win against Inter Baku at the San Mamés Stadium in the third qualifying round of the UEFA Europa League. He netted his first top-flight goal on 13 February of the following year, equalising an eventual 4–2 away loss to Real Madrid.
Eraso returned to Leganés on 24 July 2017, with the side now competing in the top division. He went on to make 215 competitive appearances over two spells at the Estadio Municipal de Butarque, being relegated in 2019–20.
On 4 July 2022, Eraso moved abroad for the first time in his career, with the 32-year-old signing a two-year contract with Cypriot First Division newcomers Akritas Chlorakas. On 12 July of the following year, he returned to Spain and its second tier after agreeing to a deal at Amorebieta.
↑Martínez de Zúñiga, Uxue (12 May 2020). "Tajonar, la cantera de España"[Tajonar, Spain's youth system]. Diario AS (in Spanish). Retrieved 27 April 2022.
↑"Contrato de Javier Eraso"[Javier Eraso's contract] (in Spanish). Athletic Bilbao. 1 July 2015. Archived from the original on 28 August 2017. Retrieved 1 July 2015.
↑Martín, Francisco Javier (11 July 2024). "Javi Eraso se retira del fútbol"[Javi Eraso retires from football]. Diario AS (in Spanish). Retrieved 27 February 2025.