The Sea Eagles appointed club legend Kieran Foran as their interim coach for the remainder of 2026 after firing Seibold on Friday night, only three games into the new season.
Seibold had been put on notice as Manly finished 2025 out of finals, before their winless start through the opening month proved the final straw.
"We wanted to back the coach and we wanted to back his coming into this season with a pre-season under his belt, let's turn it around. We just didn't see that progression," Manly chairman Scott Penn said.
"As a club, we couldn't afford to be, in three weeks time, 0-6. We felt we had to make a call quickly."
Penn, Foran and chief executive Jason King fronted a snap press conference at Brookvale Oval on Saturday morning, stressing there was no strict timeline on appointing Seibold's full-time successor.
Foran retired last season and was only four months into his first assistant-coaching position at Manly, but will be considered for the full-time role from 2027.
Ex-Parramatta coach Brad Arthur, club legend and Brisbane assistant Matt Ballin and St George Illawarra assistant Mick Ennis are thought to be in the frame.
Ballin is untested as an NRL head coach but has the support of the club's old boys, having won two premierships alongside King and served on Des Hasler's coaching staff.
He is also the only one of that trio to have played for the club, which could impact thinking given Manly have only ever won the premiership when coached by an ex-Sea Eagle.
"It's not mandatory, but there's certainly history," Penn said.
"We have a very proud history, we know what our values are, we know that we expect success and and we haven't delivered that over the last 10 years."
Current Leeds Rhinos boss Arthur led the Eels to the 2022 grand final and was an assistant in 2013 when Manly last made the decider.
The other potential option is Ennis, on Manly's coaching staff as recently as last year while being sized up as Seibold's long-term replacement.
Ennis said on Friday night's Fox Sports coverage that he had not yet been formally approached.
"In terms of longer term arrangement, it's very early days," King said.
"Once we've had time for this all to settle in, we're focused on supporting Kieran as best as we possibly can.
"Then think about what's an appropriate process to go through to think more broadly beyond 2026."
One thing that is certain is that Manly cannot afford another three-and-a-half seasons treading water as they did under Seibold, making finals only once.
A changing of the guard looms at Brookvale, with just nine players locked in beyond the end of next season and Manly now 15 years on from their last premiership.
Highly-touted half Joey Walsh has currently been left to develop in NSW Cup and will become a free agent in November if not re-signed in advance.
He, Simione Laiafi, Onitoni Large and Hugo Hart are viewed as big prospects, with Tolu Koula, Lehi Hopoate and Haumole Olakau'atu all still relatively young.
"We've got to get results. We feel like we have the right resources to do that," Penn  said.
"We've got the best junior talent coming through that we've had probably really since Foz (Foran) and Cherry (Daly Cherry-Evans) and Jamie Buhrer and Jared Waerea-Hargreaves, that was back in about 2009, was our last golden period of juniors coming through the system.
"We'll go through an orderly process to look at who's available in an orderly timeframe."
