Ivan Cleary says Brent Naden must earn back trust at the Panthers after the Penrith coach ruled him ineligible for the first month of the season.

Following the completion of NRL and World Anti-Doping Authority (WADA) investigations, Cleary has told Naden he won't be considered for NRL selection until at least round five after his positive test to cocaine hours after last year's grand final.

Naden has already served a back-dated one-month suspension, in line with the new WADA rules once it was found he took the drug recreationally and not for performance-enhancing reasons.

The 25-year-old centre has been told he is on his last chance at the club and was also recently served a suspended $20,000 fine.

He is continuing to work through mental health and rehabilitation programs, which also helped him qualify for the reduced WADA suspension.

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Naden's selection ineligibility is not an official club sanction but a stance taken by Cleary and his coaching staff after consultation with Penrith's senior playing group, including new captains Nathan Cleary and Isaah Yeo.

Naden has accepted the punishment and is in a good head space according to Cleary, with the Wellington junior still permitted to train and play trial and reserve grade matches.

"Considering what happened going into a grand final and amount of work that everyone puts into that, there was a lot of question marks, questions that came up," Cleary told SEN Radio on Wednesday morning.

"The most important thing for us was Brent’s welfare, but I think it’s fairly obvious that he wasn’t thinking clearly at the time.

It is important for us to recognise that Brent’s behaviour fell well short of the club’s and team’s standards

Penrith coach Ivan Cleary

"He’s gone through that initial rehab program and he's in a good headspace, he has come back in really good nick.

"But yes, I think there is definitely a level of trust that has to be earnt back."

As well as Cleary's selection stance, Naden was served a $5000 fine by the NRL for breaking the code's biosecurity rules the night before Penrith took on Melbourne in the grand final.

That fine also took into account Naden's income, as well as the sanctions handed down for other biosecurity breaches.

The NRL also found no evidence Penrith officials were aware of Naden's breach prior to him playing in the decider.

In a statement provided to NRL.com Cleary said: "This incident revealed some personal issues for which Brent has received professional guidance and continues to do so.

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"With the NRL investigation being completed, it is important for us to now recognise that Brent’s behaviour fell well short of the club’s and team’s standards.

"We acknowledge the significant role mental health issues played in his decision-making however we feel a four-game sanction is appropriate considering all circumstances."

Penrith have several options to replace Naden at right centre, including Matt Burton, utility Tyrone May and recent signing Paul Momirovski.

Both have been named to play in the club's first trial against Mounties this Saturday at St Marys.

Burton has been in the middle of a public tug-of-war between the Panthers and Bulldogs for much of the summer, with Canterbury pushing for an early release so he can take up his 2022 deal at Belmore a year early.

The highly-rated young playmaker has spent a large portion of the off-season training in the centres and is expected to challenge for a starting 17 spot out wide for round one.

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