Garner suffered a concussion at training on Tuesday, prompting confusion around the naming of their team to take on Newcastle.
It's understood the utility back-rower was ruled out by the doctor after the club entered him into the NRL's system to play in the No.11 jersey on Saturday.
That prompted the space to be left vacant on the NRL's website, with an automated system not allowing players to be named while they are in concussion protocols.
Preston Riki was subsequently elevated from the bench into Penrith's starting side, with former Wests Tigers forward Austin Dias brought onto the bench.
The head knock could not have come at a worse time for the Panthers.
Lock Isaah Yeo and second-rower Liam Martin are both unavailable to face the Knights due to State of Origin selection, as part of five Panthers in the Blues' camp.
Back-rower Scott Sorensen still has another week to serve for a shoulder-charge ban, as a result of electing to fight the sanction at the judiciary last month.
And to make matters worse, Isaiah Papali'i has suffered a knee injury which is set to rule him out for at least two weeks.
It means Riki will start in only his second NRL game, while Liam Henry has also moved from his regular position of prop into the second row.
Fellow prop Lindsay Smith has been named at lock.
While Penrith are also without NSW stars Nathan Cleary, Brian To'o and Dylan Edwards for Saturday's match in Bathurst, Newcastle are equally impacted.
Kalyn Ponga is their sole Origin representative, but Bradman Best, Greg Marzhew and Jacob Saifiti are all out injured.
The Panthers desperately need to win through the representative period this year given they sit 13th on the ladder, after losing their past three Origin-affected rounds.
The four-time defending premiers are expected to name all five Blues players for the round-13 match against Parramatta, given it is five days after Origin I.
The timing of Garner's concussion means he should be released from protocols and able to play in that match too.
But Penrith have already indicated their NSW stars won't back up in round 16, given they play in Auckland three days after Origin II in Perth.
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