Nathan Cleary has suffered a nasty lower leg injury from a hip-drop tackle by Phoenix Crossland.
Panthers medical staff confirmed with Nine's broadcast that he suffered a compound fracture.
Cleary's availability for the World Cup is over after images showed plenty of pressure placed on his ankle, which looked to have been broken.
He has been stretchered off the field with the aid of the green whistle just before half-time.
Cleary came into the match after starting on the interchange bench and looked to have a strong running game with plenty of touches and runs at the line.
Phoenix Crossland was sent from the field by the referee Gerard Sutton, leaving the Knights with only 12 men for the rest of the preliminary final just before half-time.
If the Panthers go on to win the match, the Roosters will face the four in a row champs without the game's best talent.
More to come.
