Muniain could be out for eight months

Athletic Bilbao's Iker Muniain could be out for as many as eight months after having surgery on the ruptured anterior cruciate ligament in his left knee.

The attacker sustained the injury in Athletic's 2-0 La Liga defeat to Sevilla last month, with an MRI scan revealing the severity of the problem.

On Thursday, the club released a statement confirming that Muniain had gone under the knife.

"The player has undergone surgery on the morning of May 7," it read.

"The surgery, performed by Dr. Mikel Sanchez and his team, has been to repair the injury...passing the intervention without complications. 

"The player will remain [in hospital] for 48 hours, after which, if no setbacks arise, he will be discharged home. 

"The next week he will begin his period of functional rehabilitation, estimated at seven to eight months for such an injury."