Callan Ward's season is over after confirmation of an anterior cruciate ligament injury.
The GWS icon went down clutching his knee in the first quarter of Saturday's three-point win over Richmond.
He met with a surgeon on Monday, with scans verifying a torn ACL.
Ward, 35, will undergo surgery later in June once his knee swelling has gone down.
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The injury could also mean the midfielder's playing career has come to a close.
However, the club shared that a decision is yet to be made.
"At this stage, Ward has not made any decisions regarding his playing future," GWS said in a statement on Monday.
"The club will provide further updates in due course."
Drafted by the Western Bulldogs, Ward made his AFL debut in 2008.
He joined GWS in 2012 before going on to play 267 of his 327 career games with the club.
Giants coach Adam Kingsley described Ward as a "fantastic clubman" on Saturday.
"It doesn't look great. Obviously, incredibly disappointing for our footy club ... such an important person, important player," he said.
"I don't know what it'll look like for the rest of the season, but he'll be around supporting us.
"He's a fantastic clubman, he sees the game really well, and there's no doubt that he'll add value in whatever he does. It just won't be on the field, unfortunately."