Athletic Bilbao were dealt a blow on Thursday with the news that midfielder Ander Herrera requires surgery to clear up a hernia.
The Basque club confirmed on their website that Herrera, 23, had travelled to Munich for a consultation with German doctor Ulrike Muschaweck after struggling with the problem since last season.
The injury did not prevent the former Zaragoza man from representing Spain at the London Olympics this summer, but he was missing from the Athletic squad for last weekend's 2-0 home win against Valladolid in La Liga.
Herrera will undergo the operation on Friday and it is not yet known how long he will be on the sidelines. His teammate Fernando Amorebieta is currently recovering after undergoing surgery at Muschaweck's clinic in July. The Venezuelan international defender was back in normal training at the club's Lezama base on Thursday, though, and is close to a return to action.