Nathan Cleary will seek specialist advice in the hope he does not require surgery to fix a shoulder injury that could jeopardise Penrith's premiership charge.

Hours after NSW coach Brad Fittler declared Cleary as "pretty unlikely" to be fit for Origin III, Eels star Mitchell Moses declared himself ready to step into the interstate arena as he and South Sydney veteran Adam Reynolds shape as the most likely replacements.

Cleary played 70 minutes with what is feared to be a partial dislocation suffered early in Sunday night's series-clinching 26-0 win for NSW, with Penrith now planning a surgical consult on the star No.7.

NRL.com understands that surgery has not been ruled out, with a best-case scenario of rehabbing the injury and playing through the pain also on the cards.

Should Cleary have to go under the knife, a lengthy rehab period looms.

Match Highlights: Maroons v Blues

Post-season surgery however may also be a possibility, pending the advice given over the next few days.

Cleary is self-isolating per Apollo protocols after playing in Origin II, with a definitive verdict on his injury to come on Wednesday at the earliest.

Penrith's decision to refuse early release requests for Matt Burton to join the Bulldogs now look set to pay off, with the boom playmaker offering a handy halves replacement should Cleary be sidelined for a significant period of time.

Speaking on SEN radio, Fittler was pessimistic about Cleary's chances of playing in Origin III, with the Blues squad for the July 14 clash to assemble from next Monday.

Fittler refused to be drawn on potential replacement options if Cleary is scratched, but pointed to this weekend's NRL clashes that will put the likes of Moses, Cody Walker and Reynolds on show.

The evolution of Nathan Cleary

Should Cleary be ruled out his Panthers teammate Jarome Luai could also shuffle to halfback as he has done at club level, with utility Jack Wighton or Walker to come in at five-eighth.

However, Moses and Reynolds offer the two most compatible replacement options with similar game management and goalkicking skills as Cleary.

Fittler has had Moses in Origin reckoning before and is a fan of the Parramatta playmaker having first combined for Lebanon at the 2017 World Cup.

Now 26 and with 165 NRL appearances to his name, Moses told reporters he believes he has developed into a representative halfback in recent years despite wearing criticism over the Eels poor finals record.

"You would like to think [I'm ready for Origin]. If I wasn't ready by now I would be kidding myself I guess," Moses said.

"I just feel like I'm a bit more in control of my game at the moment. Just controlling the boys and getting them around the park and picking my times when to inject myself into games.

"I'm getting a good level in my game. When to run, when to kick and when to pass - that's probably where I have grown a bit more."

Moses and Luai will square off in Friday's Eels-Panthers showdown as two of the NRL's most in-form playmakers.

Burton has replaced Cleary in Penrith's scrumbase with Fittler no doubt a keen observer when Moses stakes his claim for an Origin call-up, pending the injury verdict on Cleary in the meantime.

"I got along with [Fittler] really well," Moses recalled of his impressive 2017 tournament for Lebanon.

"I loved playing underneath him. He was massive for my game back then.

"He's a good operator and what he's done with the Blues this year, you can see the footy they are playing is unbelievable. They're all on the same page. It's a credit to him.

"They're just playing with a lot of energy and everyone knows their role, that's the biggest thing. Everyone is in sync, it looked like a team that's been training all year."