Garrick had become a target for Newcastle after impressing in his stints at fullback, as part of a move that would have allowed Kalyn Ponga to shift to five-eighth.

However Garrick has since delivered some much-needed good news for Manly, with paperwork lodged with the NRL on an extension that will keep the 25-year-old at the club until the end of 2027.

"The fact is that Reuben is an important player for the future," Mestrov told AAP.

"He was one of the best performers last year and we've decided to see what he can do in the centres.

"He gets the opportunity over the next four years.

"Culturally he is very important to the club and is a real leader."

Garrick's move means he will likely partner Tolutau Koula in the centres next year.

Manly will need to find a winger to start the season, with Christian Tuipulotu set to play on one edge while speedster Jason Saab will miss the opening months recovering from knee surgery.

Garrick's re-signing makes him the highest profile player to commit to Manly since the ugly exit of coach Des Hasler in October.

The Sea Eagles have endured two months of critical headlines, with dramas surrounding Hasler's exit, staffer Kristie Fulton's departure and talks of a player split.

But officials are hopeful Garrick's signing will help provide some light at the end of the tunnel.

Anthony Seibold will formally be announced as the club's new coach in coming weeks, and will likely arrive towards the end of November.

Shane Flanagan is poised to take the opening weeks of pre-season training, with Seibold still finalising his exit from England rugby.

Jim Dymock will also join as an assistant, while Manly are close to announcing a new head of performance after Don Singe's exit.

Saab, Sean Keppie and wrecking-ball Haumole Olakau'atu have also extended deals in recent weeks.

Jake Trbojevic has publicly reaffirmed he and his brother Tom's commitment to the club, while Daly Cherry-Evans has insisted the players are united.

"The players have clearly brought into the vision of where the club wants to go, and that's back to where we all see Manly - at the top of the table," Mestrov said.

"We realise we have a lot of work to do. That is a goal.

"But from a player perspective they have understood the changes and brought into the changes."

Australian Associated Press