Morgan confirmed his immediate exit on Friday after the 29-year-old was finally convinced by doctors his chronic shoulder issue was a career-ending one.

The playmaker was confident after a strong preseason he'd put questions over the health of his shoulder aside, believing he had plenty more to give after four years of injury hell.

The hero of the Cowboys' fairytale run to the 2017 grand final without Johnathan Thurston, Morgan was meant to assume the superstar's throne not just in Townsville but for Queensland and Australia.

However injuries restricted him to just 39 NRL games in the three-and-half years since, stopping him from playing his best and returning the Cowboys to the finals.

"Once I got through the preseason ... those sort of doubts about it had disappeared because of the work that I put in," Morgan said.

"It was disappointing - I got it to a point where I was extremely confident and comfortable with it and unfortunately, it didn't hold up."

Debuting in 2010, Morgan played 168 NRL games, starring in North Queensland's historic 2015 premiership.

The playmaker's flick pass to set-up Kyle Feldt's try to level the scores after the fulltime siren in the 2015 grand final will live long in the memories of Cowboys fans and rugby league folklore.

He is midway through a lucrative contract and is set to receive a multi-million dollar payout after the troublesome injury flared again after feeling a "massive crunch" in his shoulder during the Cowboys' second-round clash against St George Illawarra.

Morgan revealed at the time it didn't feel great and after several scans and meetings with specialists, it was time to hang up the boots.

"This is not the way I envisioned my career finishing, but I'm retiring knowing I gave myself every opportunity over the last 12 months for my shoulder to be strong enough to continue playing," said Morgan, who played 12 times for Queensland and Australia.

"Unfortunately, the end result was out of my control.

"Even though I'm hanging up the boots at 29, I'm extremely proud of everything I achieved over the course of 12 seasons as an NRL player."

Cowboys coach Todd Payten, who worked with Morgan both as an assistant and head coach, said his impact on the game and region was difficult to quantify.

"It's hard to put into words," Payten said.

"He's born and raised, come through the junior system, played in the U20's grand final, played in two grand finals here for the club ... he's the Cowboys through and through.

"He's been the heart and soul of this place for a long ... and he's always welcome inside this building."

Cowboys boss Jeff Reibel said his off-field impact had been just as crucial.

"His leadership around our club and his care for not only his teammates, but everyone at the Cowboys has been inspiring," he said.

"His toughness and tenacity to be able to endure what he has over the last couple of seasons should be admired - he has looked under every last rock and has gone through a lot of pain to reach the point he has today.

"Michael Morgan will be remembered as one of the greatest to ever take the field for the North Queensland Cowboys."

Australian Associated Press