In short:

Panthers coach Ivan Cleary says son Nathan had come into Sunday's preliminary final with a broken right foot.

Nathan then suffered a horror compound fracture to his left ankle, with Ivan saying he will need surgery on both injuries.

What's next?

Injuries to fellow Panthers stars Dylan Edwards and Isaah Yeo could mean bad news for Australia at next month's Rugby League World Cup.

Nathan Cleary will require surgery on both feet, with his father Ivan revealing the superstar halfback had been playing on a broken right foot before suffering a compound fracture of his left ankle.

In a gruesome aftermath to the Panthers' 22–14 preliminary final loss to Newcastle, Penrith exited with Dylan Edwards playing through a ruptured PCL, Isaah Yeo a ruptured pec, and Blaize Talagi off with an Achilles rupture.

The injuries ultimately cursed the Panthers after they led the Knights 14–6 at half-time and will likely have long-term ramifications for Australia in the end-of-season World Cup.

Penrith had hoped to get Cleary through Sunday's game unscathed after keeping him and his injured right foot on the bench for the opening 25 minutes.

But 10 minutes later the superstar halfback was exiting the field on the back of a medicab sucking on a green whistle, after a hip-drop tackle from Newcastle hooker Phoenix Crossland.

Crossland was sent off, with Cleary's ankle also dislocated and his mother, Bec, among those in the stands in tears.

"He watched the game in the ambulance, but it made him feel worse probably," coach and dad Ivan Cleary said.

"I went and saw him at half-time and saw the whole crew and my family were in there. That was a bit hard, it was a bit emotional. But the show goes on."

Cleary also confirmed his son had been battling a broken bone in his right foot, after Penrith had previously been coy on the nature of a "stress-related bone issue".

The Penrith halfback had been in doubt for Sunday's match in the lead-up, after he limped through the end of their week-one win over the Sydney Roosters.

"He'll have to get the other foot done as well, because that was broken as well," Ivan Cleary said.

"That's why I was even more emotional with what happened to him because I knew what he went through to get himself right to play today."

Beyond their halfback, Edwards was hurt when making a break in the opening half and Talagi limped off with 13 minutes to play.

Yeo, meanwhile, returned from a ruptured pec to play in the finals. He will now require surgery, with the Kangaroos captain in doubt for the World Cup.

AAP