Cronulla Sharks head coach Shane Flanagan has resigned just weeks after he was de-registered by the NRL.

Flanagan, whose resignation is effective immediately, was de-registered for flouting his 2014 suspension for his part in Cronulla’s peptides scandal.

The Sharks were fined $800,000 for their part in the supplements saga.

Flanagan was the Sharks’ head coach for seven years. He started as assistant coach in 2007 and became head coach late in 2010.

“This was obviously one of the toughest decisions of my 36-year rugby league career to resign from the head coaching role at Cronulla,” he said in a joint statement with the club on Monday.

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

Flanagan’s career came tumbling down after an NRL integrity unit investigation – which was examining the club’s self-reported salary cap irregularities – uncovered evidence he had communicated with Sharks officials during his 2014 ban.

He was banned for 12 months – later reduced to nine months – for his part in Cronulla’s illegal supplement program under rogue sports scientist Stephen Dank during the 2011 season.

Under the terms of his ban, he was not allowed to have any involvement or contact with the club.

The NRL gave Flanagan and the Sharks until the end of January to respond to its de-registration notice. Flanagan said he still intended to do so.

But his decision to resign was in the best interests of the club and the players, and would allow them to prepare for the 2019 season without constant speculation and uncertainty about who their head coach would be.

“Without doubt, I will hold the entire 2016 playing squad, staff, supporters and unforgettable achievement to deliver the club it’s first premiership, forever in my heart,” he said.

“I want to single out and thank the incredibly loyal Sharks supporters for their on-going support and last but certainly not least, I want to thank rugby league fans in general for their overwhelming support and messages over the years and more so over the past month.”

Club chairman Dino Mezzatesta said Flanagan would hold a special place in the Sharks’ history.

“Shane was our first premiership winning coach, he is the coach of our team of the half century and he has given exceptional service and dedication to our club,” he said.

Flanagan leaves as the Sharks look to the 2019 season without a guernsey sponsor and facing serious financial stress.

Sharks assistant John Morris has been appointed interim head coach, as the club’s first trial against Manly looms in just five weeks. Mezzatesta said there would be an announcement on a permanent replacement in coming weeks.

-with AAP