Iker Undabarrena Martínez (born 18 May 1995) is a Spanish professional footballer who plays as a defensive midfielder for Malaysia Super League club Johor Darul Ta'zim.

On 28 November 2012, aged 17, Undabarrena made his official debut with the main squad, coming on as a substitute for Igor Martínez in the 77th minute of a 2–0 away win against Hapoel Ironi Kiryat Shmona in the campaign's UEFA Europa League.

[5] He appeared in almost all of the domestic league matches until 13 February 2016, when he suffered a rupture of the anterior cruciate ligament in his left knee during a fixture against Real Valladolid, requiring a lengthy rehabilitation.

Despite making a successful return to the B-team with ten appearances and one goal between March and May (including two in the promotion play-offs), Undabarrena was released by Athletic Bilbao on the expiry of his contract on 1 July 2018, ending a 13-year association with the club.

[10] On 3 July 2018, free agent Undaberrena agreed a deal to join second-tier Tenerife (at the time coached by former Athletic Bilbao player Joseba Etxeberria) on a three-year contract.