Nathan Cleary's World Cup availability is over after he suffered a compound fracture in the preliminary final, Panthers medical staff confirmed to Nine's broadcast.
The injury came in a hip-drop tackle by Phoenix Crossland shortly before half-time.
Cleary was carried from the field on a stretcher with help from the green whistle.
He had entered from the interchange bench and made several strong runs at the line.
Referee Gerard Sutton sent Crossland from the field, leaving Newcastle with 12 players for the remainder of the preliminary final.
If Penrith wins, the Roosters will face the four-time defending champions without Cleary.