A month after being provisionally deregistered by the NRL for continued contact with the club during his 2014 ban, Flanagan conceded his nine-year reign was over.

Five weeks before the Sharks' first trial match and seven weeks out from the season start, Flanagan said his decision was for the club's best interests but he still intended to respond to the NRL's show-cause notice before the January 31 deadline.

Morris declared last week he wanted the job long-term if Flanagan didn't return, but the club said on Monday it would make an announcement on the role "in coming weeks".

They should have no shortage of potential candidates to guide a seasoned squad capable of challenging for the title following last year's preliminary-finals exit.

Despite his controversial stint at Manly, Trent Barrett would likely be among the favourites if Cronulla look outside, but Morris is well liked and was chosen ahead of fellow assistant Jim Dymock as interim earlier this month.

Anthony Griffin is also available after being sacked by Penrith last year, while NRL assistants Adam O'Brien, Jason Demetriou and Cameron Ciraldo are considered next to step up.

A number of high-profile NRL coaches are also off contract at the end of 2019, including Brad Arthur and Paul McGregor.

Flanagan admitted his second heavy sanction from the NRL had been hard to deal with, prompting him to inform the club of his intentions late last Friday.

"This was obviously one of the toughest decisions of my 36-year rugby league career to resign from the head coaching role at Cronulla," said Flanagan.

"The last month has taken an enormous mental and emotional toll on my family and myself.

"I intend on responding to the notice issued by the NRL, however I have made this decision in the best interests of the club and the players to allow the best possible preparation for the 2019 season without constant speculation and uncertainty as to who their head coach will be."

Sharks CEO Barry Russell is overseas and will return late Wednesday with the job of finding someone to fill the hole left by Flanagan.

After 185 games in charge over eight seasons, Flanagan was on track to become the club's longest-serving coach this year and was named as mentor of their team of the half century in 2017.

He twice brought the club back from the bottom of the ladder, the first time when he took over in 2010 and then helping them rebound from the peptides saga to their drought-breaking 2016 title.

However it was the ASADA drama that proved his downfall, caught breaking the terms of his 2014 ban when emails uncovered as part of the club's self-reported salary cap scandal showed him communicating with club officials.

Australian Associated Press