Athletic Bilbao forward Iker Muniain has been ruled out for at least six months with a cruciate ligament injury.
After tests were performed on the Spanish playmaker on Tuesday, the club's official website issued a statement saying: "A torn cruciate ligament has been detected in his left knee."
Muniain will now miss his side's Copa del Rey final against Barcelona, as well as the start of the 2015-16 season. Athletic said his recovery is likely to take "six to seven months," giving him an expected return date of October or November.
The 22-year-old, who has started in 25 of his team's 29 league matches this season, was stretchered off on Saturday during his side's 2-0 defeat at Sevilla after colliding with Ever Banega.
Midfielder Ander Iturraspe also picked up a leg muscle injury in the game, and his condition is being monitored.
Muniain has one senior international cap and won the European Under-21 Championship with Spain in 2011 and in 2013.