After losing star James Maloney to Super League, the Panthers are promoting from within to find a halves partner for State of Origin star Cleary.

However, Girdler believes it's a dangerous exercise with no clear replacement for Maloney - the man who set up 18 of Penrith's tries in 2019 compared to Cleary's nine.

Young guns Jarome Luai and Matt Burton will both feature in Saturday's trial against the Wests Tigers in a bid to push their case for the No.6 jersey.

However, Girdler, who played more than 200 games for the club, is not convinced either of them have what it takes to replace Maloney.

"Nathan likes to play within structures and I think sides need to be able to play in and out of structure," he told AAP.

"So someone needs to come through their system and be the guy who can create something out of nothing."

"I thought (Penrith have) probably regressed in the last couple of years. A lot of people talked about their defence, but I thought their attack really struggled last year."

Luai partnered Cleary in the halves for an under-20s title with Penrith back in 2015 and is tipped to be the front-runner for the position.

His weight on the club website is listed as 88kg, but Girdler doesn't believe he is up to the rigours of first-grade for a full season.

"I saw little bits of him last year and he looks like a player but I'm not sure you're not going to get 24 or 26 rounds out of a young 85 kg five-eighth," he said.

"I like young Burton. I think he's a guy who can come up and make his presence felt, but that's a transition for those guys over time to settle into a role as a fulltime NRL player."

The addition of hooker Apisai Koroisau to the spine along with assistant coach Trent Barrett working with the halves is intended to spark Panthers' attack in 2020.

But for it to work, Koroisau needs license to run.

"I think Api will help that to a degree, but they need to make sure he's allowed to play the way he played at Manly," Girdler said.

"He was so effective, flat and fast and through the middle and he was able to jump out and take opportunities.

"From the Penrith I saw in 2019 they don't play like that. They work to a certain area and look for the long shift and it really was predictable and unsuccessful.

"I think Penrith are going to be one of those teams this year who need to be at their best every week to compete with the better sides."

Australian Associated Press