The signing of the 32-year-old centreback, a Spain international, on a contract until 2025, continues the Catalans’ recent policy of hiring experienced players at zero transfer cost.

Barcelona signed Manchester City captain Ilkay Gundogan in a similar fashion last week and acquired Chelsea defender Andreas Christensen and AC Milan midfielder Franck Kessie after their contracts expired last summer.

“(Martinez) will sign for two seasons, until June 30 2025, and will have a €400 million (US$435 million) release clause,” said the Spanish champions in a statement.

Martinez, who came through at Real Sociedad and played for them for seven seasons in the top flight, moved to Athletic in January 2017.

Athletic Bilbao paid his €32 million (€$35 million) buy-out clause, which remains a club record fee.

Martinez played 177 times for Athletic, scoring eight goals and winning the Spanish Super Cup in 2021, as well as reaching two Copa del Rey finals.