Replacing Ponga the No.1 priority

Ponga is facing the prospect of surgery and at least half a season on the sidelines after rupturing a ligament in his foot during Newcastle's 36-12 loss to Canterbury on Sunday.

"Kalyn had scans on Monday morning confirming he has a Lisfranc injury," Knights football director Peter Parr said in a club statement on Monday.

"The next steps will include seeing a surgeon and setting an injury-management program.

"Unfortunately, at this stage it appears to be a long-term injury, with a return to play likely to be months rather than weeks."

In Ponga's absence, O'Brien said his options were veteran outside back Dane Gagai, who is more renowned as a centre, or young tyros David Armstrong and Fletcher Sharpe, both of whom are highly rated but yet to make their debuts in the NRL.

"We've got a young kid, Fletcher Sharpe, he's got an exciting future but he's been on an injury list for a couple of weeks now, with a hammy," O'Brien said after Sunday's defeat.

"He wouldn't be far away.

"But I guess the first thought is young Davey Armstrong ... on the whole he's done a fair job, Dave Armstrong. But we'll get Dane back next week. Whether Gags goes back there, I don't know. I'll have to have a look at it."

While Gagai has played the vast majority of his 273 first-grade games as a centre, he is no stranger to fullback, having appeared 27 times in Newcastle's No.1 jersey.

But he hasn't played as the last line of defence since a one-off game for South Sydney in 2018.

Armstrong, a 23-year-old Moree junior, showed genuine pace in the pre-season trials and has been a standout in Newcastle's NSW Cup side for the past two seasons, scoring 23 tries in 27 games. This season he has scored five tries in four reserve-grade games.

Sharpe, still only 19, is a Cessnock junior who starred in the Newcastle side that made the Jersey Flegg grand final two seasons ago.

He has has scored three tries in as many NSW Cup appearances this year.

Another alternative who O'Brien did not mention is English import Will Pryce.

Pryce has been playing five-eighth in reserve grade but his 45 Super League games for Huddersfield included 17 at fullback.

As well as finding a new fullback, O'Brien may have to replace winger Tom Jenkins, who suffered a knee injury against the Bulldogs and was unable to finish the match.

Converted back-rower Dylan Lucas may need to return to the centres.