Nathan Cleary is likely to miss the World Cup after a compound fracture and dislocated ankle in Penrith's preliminary-final loss to Newcastle.
His father, Ivan Cleary, said Nathan started with a broken right foot and will need surgery on both feet.
Isaah Yeo's availability to captain Australia is also uncertain after he delayed surgery for a ruptured pectoral muscle to play in the finals.
He said the operation could affect his start to next season.
"I don't know if I'll be available yet, I'll have to talk to the club as well because it will affected the start of next season if I was to prolong it," Yeo said.
"I'm not sure. That's a conversation for probably later on next week with Ivan and the staff. But not sure yet."
Dylan Edwards ruptured a PCL in the match and is likely to miss the World Cup.
Blaize Talagi ruptured his Achilles, ruling him out of Samoa's campaign and leaving him facing a lengthy rehabilitation.
Penrith failed to score after halftime against 12 Knights players, despite spending more than 80 per cent of the second half in attack.
"I can't really explain what happened in the second half," coach Cleary said. "We were probably just falling apart a little with injuries."