Athletic Bilbao have confirmed forward Iker Muniain has suffered knee ligament damage during Thursday’s Europa League loss to Zorya Luhansk.
The 24-year-old has ruptured the anterior cruciate ligament in his right knee and now looks set for a lengthy spell on the sidelines.
However, the Basque club did not put a timescale on the forward’s layoff and say that further tests need to be carried out before a timetable is drawn up.
Two years ago, Muniain missed six months of action following a torn cruciate knee ligament sustained against Sevilla.
He was stretchered off late in Thursday night’s defeat to the Ukrainian side at San Mames, which leaves Athletic with just one point from their opening two Europa League group games.