Rosa injured his thigh in last week's loss to Port Adelaide, and was forced to go under the knife after it was found he had compartment syndrome.
The 26-year-old's injury comes at a bad time for the Eagles, who are likely to be without ruckman Nic Naitanui (groin), midfielder Daniel Kerr (knee) and forward Mark Nicoski (hamstring) for the round-one clash with Fremantle.
Star recruit Sharrod Wellingham has already been ruled out with an ankle injury, but wingman Andrew Embley is expected to recover from a hamstring injury.
Rosa missed West Coast's 2011 finals campaign with a knee injury, while he also broke his jaw and fractured his collarbone in separate incidents last year.
But his biggest heartbreak was missing out on selection for West Coast's 2006 Grand Final triumph despite playing 15 games that year.
