Penrith second-rower Viliame Kikau has been ruled out for up to six weeks of rugby league after undergoing scans on his right knee on Monday.
Kikau suffered the injury early in Saturday's NRL trial win over South Sydney - the Panthers' first hitout of the season.
"He (Kikau) will rehab strongly and come back better than ever," Panthers boss Phil Gould said on social media on Monday.
With the Panthers' NRL opener against Parramatta not until March 16, the Fijian international may only miss three games of the season.
Returning coach Ivan Cleary could have Kikau back in time for the club's round-four clash with the Wests Tigers.
Kikau's absence will be an early test of the Panthers' depth, with former South Sydney forward Tyrell Fuimaono their only summer signing in the backrow.
Lock James Fisher-Harris could be an option to shift to the edge, opening a spot for ex-St George Illawarra middle forward Hame Sele.
The Panthers round out their pre-season preparations with a trial against Parramatta on Saturday, before meeting the Eels again at home in round one.
