TAI Tuivasa gambled away $20,000 the night before he walked out on the Sydney Roosters, quit rugby league and looked for a change of life in boxing.

Set to make his UFC debut at Qudos Bank Arena this Sunday, Tuivasa was once ranked alongside Tricolours young guns like Dylan Napa, Boyd Cordner and Roger Tuivasa-Sheck.

Yet for the first time, the rising heavyweight has told The Daily Telegraph how his problems with gambling convinced him to walk out on the code in favour of fighting.

Quizzed on why he quit the Roosters, Tuivasa replied: “Because the night before, I did my arse at Star Casino.

“Lost about $20,000 on the pokies.

“At one point in the evening, I honestly believed I’d make a million dollars. Yet when I finally walked out, I had nothing — not even enough money for a cab.

“And that’s when I decided I had to get out of rugby league. Get back with my family and a different way of living.”

And so, he did.

media_camera Tai Tuivasa has made the switch from the rugby league field to the octagon.

Tuivasa phoning U/20s coach Jason Taylor that next morning to say he quit.

And while not the first Sydney footballer to be led astray, the 24-year-old refuses to blame either the Roosters or rugby league’s oft debated culture for his departure.

“This was about me,’’ he insists. “I was living in Maroubra with a few other boys; punting, drinking, all that sort of shit.

“There isn’t a lot of science behind it.

“One bloke does something, so three more of you do it.

“It happens.

media_camera Paul Gallen sparring with Tai Tuivasa last week. Picture: Grant Trouville

“But I just realised, for me, it couldn’t continue. I had to go home to family in western Sydney.”

Certainly the Roosters knew they were losing an NRL player.

Initially signed to Penrith Harold Matthews, the Tricolours swooped in 2010 through then recruitment guru Peter O’Sullivan.

“And I still have no doubt Tai’s an NRL player,” O’Sullivan told us two years later, when the prop walked out. “The kid is incredibly athletic, skilful and has a good footy brain.”

Which is why, initially, concerned coach Jason Taylor suggested Tuivasa just take a few days off.

“But I was fairly blunt,” the fighter continued. “I said ‘mate, I’m not coming back’.”

And he hasn’t.

media_camera Then-Sydney Roosters junior and MMA fighter Tai Tuivasa, aged 17, at Redfern PCYC.

Instead, the 140kg slugger has built up an imposing MMA resume that sees all seven wins arrive via first round KO.

And now this Sunday, five years after quitting rugby league, he makes his anticipated UFC debut against tattooed Texan Rashad Coulter.

“And this UFC plan, it’s always been there,’’ he stresses. “I would never have just given up on rugby league if there wasn’t something else in place.

“Or if I didn’t believe in my ability as a fighter.

“I’m not that stupid.

“So the idea of fighting, it had been in my mind for some time. That night at the casino, it was my tipping point.”