GREATER Western Sydney defender Adam Kennedy will miss the rest of the season after it was confirmed he ruptured the ACL in his left knee.

In another blow, tough onballer Jacob Hopper broke a finger in the same game and requires surgery. The timeframe he will miss is unclear at this stage.

Kennedy landed awkwardly on his left leg in the 23-point loss to St Kilda on Friday night at Etihad Stadium after going up in a marking contest with GWS co-captain Phil Davis and former teammate Josh Bruce in the first quarter.

The 24-year-old spent the rest of the term on the sidelines while being tested and was ruled out for the rest of the game. 

Medical staff at the Giants will consult with specialists to determine how to proceed. 

"This is devastating news for Adam who'd started the season very strongly. We're confident that Adam will approach his rehabilitation with the same diligence and energy that he does every other aspect of his football," GWS head of athletic performance David Joyce told gwsgiants.com.au.

"He's a really popular member of the playing group and the whole club is right behind him."

Losing the backman means Leon Cameron's team will be further exposed in defence, with Nick Haynes (hamstring) and Matt Buntine (knee) also sidelined for an extended period. 

Kennedy has played 83 games since being pre-listed by GWS. His contract expires at the end of this year. 

Hopper's loss is also damaging, considering former Tiger Brett Deledio yet to play a game for his new club as he struggles with a persistent calf injury, while Ryan Griffen and Will Setterfield need to overcome ankle issues. 

Cameron flagged the possibility of bringing banned midfielder Lachie Whitfield straight into the side for next Saturday's match against Collingwood at Spotless Stadium.