Papali'i became the Panthers' first marquee signing in five years on Thursday, signing a three-year deal for 2025 after being told by the Tigers he could move on.
Penrith have traditionally built from within in recent years, operating on a long-term plan of knowing which players they can afford to lose ahead of time.
But Fisher-Harris's sudden departure prompted the three-time defending premiers to venture outside of their squad, in a bid to beef up their pack for 2025 and beyond.
David Fifita was Penrith's clear first target, before he overlooked them a fortnight ago and subsequently backflipped on the Sydney Roosters to stay at Gold Coast.
Papali'i has the potential to play as both an edge and a middle, after starring for the Eels as a second-rower before spending time at lock for the Tigers.
The most likely situation for the Panthers is to play Papali'i as a second-rower next season, moving Sorensen to the bench while primarily acting as a middle forward.
Scott Sorensen is happy to play in the middle again to accommodate new signing Isiah Papali'i. (Dan Himbrechts/AAP PHOTOS)
Sorensen said he had not spoken to coach Ivan Cleary about Papali'i's signing, but could see the logic in having him return to a role he has previously filled.
"I've played in the middle (before), so everyone probably just looks at me to roll back into the middle," Sorensen told AAP.
"I'm completely happy and comfortable to do."
Sorensen played primarily as a middle off the bench for Penrith in 2021 and 2022, before becoming a left-edge second-rower when Viliame Kikau left at the start of last year.
"I was really enjoying my footy in the middle," Sorensen said.
"And then I got put out on the edge and I'm really enjoying it out on the edge.
"Who knows what Ivan's got cooking or what his plans are. But if that means I play a little bit more in the middle or if Papali'i is there, I'm happy."
Papali'i's signing also means Angus Crichton is no longer in the Panthers' sights, after they made inquiries with his management earlier this month.
He is now most likely to stay at the Roosters if he remains in the NRL, unless a deal in French rugby is finalised.
Papali'i's Tigers exit is also expected to be the first of several in a roster overhaul at the joint-venture.
The 25-year-old left Parramatta at the end of 2022, but has failed to recapture the same level of form since arriving at Concord.
"This is purely about getting our salary cap in better shape, and it's not a simple thing to do," said Tigers chief executive Shane Richardson.
"Effective salary-cap management is so important in this business, and it's a puzzle you simply must get right if you want to be a successful NRL club."
Richardson has headed to England in recent days to try to offload some of the club's highest earners and set Marshall up for success.
The Tigers have slumped to a 2-8 start under Benji Marshall, and playmaker Jayden Sullivan is likely to follow Papali'i out the door ahead of Jarome Luai's arrival next year.
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