GWS could be without top pick Will Setterfield for the entire season, with the club believing he has torn his anterior cruciate ligament.
On the eve of the season, Setterfield fell awkwardly on his left knee in the third term of GWS's practice match against Sydney.
A stretcher was called for the 20-year-old, but he was helped off by club trainers.
Assistant coach Lenny Hayes confirmed after the game that Setterfield would go in for scans today to confirm what is believed to be a torn ACL.
The tall midfielder was drafted with pick five in the 2016 AFL draft after coming through GWS's academy, but has only played two games for the Giants.
His 2017 season was also wrecked by injury.