Isaah Yeo was unsure whether he could play in the World Cup after Penrith's 22-14 preliminary-final loss, and said he would discuss surgery with his club next week.
Yeo had played through the finals with a torn pectoral muscle.
Penrith also lost Nathan Cleary, who was taken to hospital before half-time with a compound leg fracture. The injury rules him out of the World Cup and is expected to require a long recovery.
Cleary said Dylan Edwards ruptured his PCL in the first half but continued playing, leaving his World Cup availability in doubt.
"Dyl Edwards ruptured his PCL in the first half tonight, (he) played on," Cleary said in his post-match press conference.
"We probably just fell apart a bit.
"I think that's why I was even more emotional on what happened to him (Nathan's injury), how hard he worked and what he put himself through to get himself to play today."
Blaze Talagi ruptured his Achilles in the second half and was taken from the field. The injury ends his World Cup hopes with Samoa, while Luke Garner moved to the centres.
The Knights played most of the match with 12 men and still won. Ivan Cleary said: "I wanna pay full credit to the Knights and their supporters, just a great day for their club and sets up a pretty good Grand Final,"