The 25 year-old missed much of last season due to injury but has featured in 11 LaLiga games this term, although Athletic is hovering dangerously close to the relegation zone.

Muniain has shown fine form, though, contributing four goals, including finding the net in Athletic's 1-1 home draw against Real Madrid in September.

The versatile forward, who has spent his whole career at Athletic, won his sole Spain cap in 2012.

The club confirmed Muniain's new deal does not include any release clause.