Ivan Cleary believes Penrith's tough NRL run since State of Origin will have them better prepared for the finals.

Having lost only once this season up to Origin III on July 13, the defending premiers have lost twice in the five matches that followed, with star halves Jarome Luai and Nathan Cleary largely absent due to injury and suspension respectively.

The Panthers squeaked past Wests Tigers immediately after the Origin period, and have then faced Cronulla, Parramatta, Canberra and Melbourne in a gruelling run towards finals.

Cleary's team face a resurgent South Sydney on Thursday at Accor Stadium in a mouth-watering clash between last year's grand finalists, with the Rabbitohs coming off a 26-0 thumping of the Eels.

The coach is still without his first-choice halves pairing while Taylan May (shoulder) and influential forward James Fisher-Harris (suspension) are also sidelined.

Dylan Edwards missed last weekend's 16-0 loss to Melbourne with a sternum injury while NSW Origin forward Liam Martin came off during the defeat with an ankle issue.

Both have been named to play but Cleary said a final call on the pair's availability wouldn't be made until game day.

The testing period is unlikely to deny Penrith this year's minor premiership, which can be confirmed if they beat Souths, and Cleary expects the Panthers to come out of their testing times better for the experience.

"We've had a really difficult run pretty much since Origin. We've played lots of the big teams," Cleary said.

"The last few weeks playing some guys that will get more minutes and more experience.

"It's really good actually.

"Another big one tomorrow night as well. It'll prepare us well for what's ahead."

Latrell Mitchell is expected to play for South Sydney at fullback despite an early finish to training on Monday with groin tightness.

Coach Andrew Demetriou's Rabbitohs have been boosted by the return of centre Campbell Graham (cheekbone) and front-rower Daniel Suluka-Fifita (back), while youngster Lachlan Ilias moves back into the No.7 jersey at halfback.

Cleary said beating a resurgent Souths team, who have won six of their past seven matches to sit just two points outside the top four, would take more than just stopping Mitchell's attacking influence.

"It's not just Latrell, it's probably their whole team," Cleary said.

"They're a very dangerous team. Always have been, and they're looking really good at the moment.

"We've got to try and keep them down their end of the field."