Nic Naitanui will have a traditional knee reconstruction after rupturing the anterior cruciate ligament in his right knee at the weekend.
West Coast confirmed the news on Tuesday.
It means the Eagles’ star will likely miss a year of football.
Naitanui, who’s suffered the injury before, hurt himself during the club’s great win over Collingwood at the MCG.
His absence puts a huge dint in the Eagles’ premiership chances.