Cleary did not warm up with Panthers teammates on a wet Accor Stadium on Sunday afternoon, with the halfback instead spotted going through his paces inside.
It came as the Panthers named Jack Cole and Jack Cogger to start in the halves, and Cleary on the bench.
That theoretically gives Penrith a chance to hold the superstar playmaker back and even only use him in a break-glass-in-case-of-emergency situation.
If they were to win without him, it would also give Cleary the chance of being able to play next Sunday's grand final off a three-week recuperation.
Cleary's availability for Sunday's match had been under a cloud since he limped through the final 10 minutes of the finals week-one win over Sydney Roosters.
Scans then detected a "stress-related bone issue", with Penrith not offering any further detail.
When asked on Saturday morning whether his son would be right to start, coach Ivan Cleary had been evasive in his response.
"Is he impact off the bench?" Ivan quipped.
"Nah, Nath is ready to play. He is obviously carrying an injury but there wouldn't be many players out there for any team at the moment who aren't.
"It's just that time of year. But we're super confident that all our guys are ready."
The coach then stressed on Sunday they had a "plan" for Nathan, with Penrith board director Greg Alexander indicating he would be on the field after the 20-minute mark.
"They think staying out of the rough and tumble of the opening 20 minutes will help Nathan get through this game," Alexander said on Fox League.
"And, if required, help his recovery to their next game - if there is one.
"He'll be on the field today, no matter what."
Alexander confirmed that Cleary had trained for an hour on Thursday, but said he would not take shots at goal.
That in itself will raise further questions over whether the NRL's best player will be able to deploy his in-play kicking.
Liam Henry will also start for Penrith in place of Lindsay Smith, while Scott Sorensen starts for Isaiah Papali'i.
Newcastle are as named.
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