The Panthers' next opponents Manly have also been dealt an injury blow with coach Anthony Seibold confirming five-eighth Josh Schuster will miss a second-straight game with a quad issue.
Fisher-Harris left the field after just 20 minutes in last Friday's win over Canberra and did not return.
The Panthers have named Matt Eisenhuth to start in the front row for Saturday's game but did not put a timeframe on Fisher-Harris' return until Friday morning.
"It's probably five weeks," coach Ivan Cleary said.
"As it turned out, I'm glad he didn't go back on (against Canberra) because he would've been at more risk."
Fisher-Harris has been one of the most consistent props in the NRL in recent seasons and the Panthers would have been banking on him for big games against South Sydney and the high-flying Warriors in the coming weeks.
His absence puts more strain on a Penrith forward pack that has missed Liam Martin, Luke Garner and Soni Luke - all to injury - this season as well as the departures of Viliame Kikau (Bulldogs) and Api Koroisau (Wests Tigers) at the end of last year.
Martin and Garner are due back next week while Luke returns against Manly.
Cleary urged his players to step up in Fisher-Harris' absence.
"If you look around the league there are plenty of injuries at the moment," he said.
"As a team we just have to all work a little bit harder and fill the gap.
"We lose a fair bit (with Fisher-Harris out) but I'm not trying to focus on what we don't have, it's what we do have."
Schuster, meanwhile, is enduring a turbulent start to life as a five-eighth and will finish the weekend having played only two of a possible five games to start 2023.
The former second-rower missed the opening weekend with a calf injury and his latest setback will raise further questions as to his ability to withstand the physical demands of a switch to the halves.
Youngster Kaeo Weekes will now start in the halves for the first time at NRL level, partnering Daly Cherry-Evans.
Meanwhile, Cleary has defended the Panthers after a media attack this week.
After the Panthers' win over Canberra, Cleary declared it was "good karma" the last try had been scored by Jaeman Salmon, whom Raiders coach Ricky Stuart targeted with his "weak-gutted dog" barb following the sides' previous meeting.
Media commentary in the wash-up for the game claimed Cleary's "karma" comment was the latest example of the back-to-back premiers' boastful attitude.
Cleary said while he would continue to keep a close eye on his charges, he was proud of the culture fostered at Penrith.
"The people I talk to and the people I hang out with really like the club and are happy with what we do," he said.
"I feel like we've certainly performed over a number of years now, so that's one thing.
"The work I see the boys do consistently within the community after games for example ... we're always obviously keeping an eye on it because I guess that's my job, but for the most part I'm really proud of our club and our boys."
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