Scans have confirmed Panthers forward Frank Winterstein suffered a grade two medial collateral ligament injury in Friday night's win over Wests Tigers.
The MCL tear in his right knee will see the 32-year-old sidelined for up to six weeks.
Winterstein suffered the injury in the first minute of Friday's game at Panthers Stadium and played on for several minutes before being substituted for Viliame Kikau.
Winterstein's replacement in the Panthers side to face Gold Coast Titans will be revealed when coach Ivan Cleary names his squad on Tuesday.
OAK Plus Post Game: Frank Winterstein