GWS have confirmed forward Jon Patton has ruptured his ACL for the third time in his career.
The 25-year-old suffered the incident at training on Thursday, and scans on Friday morning revealed the extent of the injury.
Patton has previously suffered two ACL injuries on his right knee in 2013 and 2014, although this time the injury occurred on his left knee.
GWS General Manager of Football Wayne Campbell told the club's website how disappointed he was to hear the news.
“This is obviously devastating news for Jon who’s a much-loved figure at our club," Campbell told gwsgiants.com.au.
“He’s shown the resilience to fight back from serious injuries in the past and we’re confident this will once again be the case.
“He has the full support of everyone at the GIANTS, and I’m sure the wider football community, as he faces this next challenge.”
Patton has played 89 AFL games in his career, for 130 goals.