Nicoski, who played every game last season and was a key figure in the Eagles' resurgence, suffered the injury in Saturday night's NAB Cup Grand Final loss against Adelaide at AAMI Stadium.
West Coast said a recovery period for Nicoski, who kicked 41 goals last season, would not be known until the 28-year-old had undergone surgery on Wednesday.
The Eagles will now start the 2012 season without two of their three leading goalkickers from last year, with Mark LeCras ruled out for the season with a ruptured anterior cruciate ligament in his right knee.
The club's leading goalkicker last season, Josh Kennedy (59), has not played this pre-season because of a foot tendon injury, while Quinten Lynch is recovering from a minor hamstring injury.
Western Bulldogs recruit Josh Hill is now expected to play a key role in a re-worked Eagles forward line, while Ashton Hams and Gerrick Weedon also battle for a spot in the round-one team to face the Western Bulldogs at Etihad Stadium.
Nathan Schmook covers West Coast news for AFL.com.au. Follow him on Twitter: @AFL_Nathan
