The Knights have confirmed the severity of Kalyn Ponga's foot injury suffered in the loss to Canberra on Friday night.
Ponga went down in the second half of the defeat at McDonald Jones Stadium.
On Saturday, the Knights confirmed he'd suffered a mid-foot sprain - known as a Lisfranc injury.
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The diagnosis rules the fullback out of the State of Origin decider in Sydney, although Newcastle are hopeful he will still play some part in their season.
"Knights Captain Kalyn Ponga underwent scans this morning to assess an injury suffered in the 2nd half," a club statement read.
"The Knights and QLD fullback has been diagnosed with a Lisfranc injury.
"Ponga will begin his rehabilitation with Knights medical staff, with the view of returning to play in the back end of the season."
A high-grade Lisfranc injury, like the one to his right foot which forced Ponga to miss 10 weeks last season, typically requires surgery.
NRL Physio reported that the prognosis may mean the 27-year-old has managed to avoid that fate this time around on his left foot.
Knights confirm Kalyn Ponga suffered a Lisfranc injury (midfoot sprain) in Round 17 - he will commence rehab with the aim to return later this season.
— NRL PHYSIO (@nrlphysio) June 28, 2025
With that recovery timeframe hopefully he avoided surgery - a moderate midfoot sprain often involves a 4-6 week return to play. pic.twitter.com/aOmEicaKWf
The Knights, who currently sit in 13th spot with a 6-10 record, have two byes over the remaining 10 rounds of the season.
While they may still hold out hope of qualifying for the finals, Ponga's injury, along with the suspected season-ending lacerated kidney and ruptured spleen suffered by Fletcher Sharpe last week, could be the final nails in the coffin for their 2025 campaign.