Nathan Cleary is expected to face six months of recovery, barring setbacks, after emergency surgery for a compound fracture.
He broke both lower-leg bones in a hip-drop tackle by Phoenix Crossland late in the first half of Penrith's preliminary final.
The Sydney Morning Herald reported heavy bleeding and concern about blood supply to Cleary's foot, prompting staff to stabilise his leg as he left the field.
Penrith medical staff compared the injury to a "bullet wound", while club sources called it the worst leg break they had seen.
Crossland was referred to the judiciary and could face suspension affecting his availability for the New Zealand Kiwis' World Cup campaign.
Ivan Cleary said in his post-match press conference: "I went and saw him [Nathan] at half-time and saw the whole crew, my family, in there. That was hard and a bit emotional,"
Penrith also lost Blaze Talagi to an Achilles injury, and Dylan Edwards ruptured his PCL in the first half, Ivan confirmed.