He was warming up on the sideline getting ready to go on against the Wests Tigers when he strained his hamstring.
He didn't want to tell any of the Cronulla coaching staff because he was desperate to play and, on top of that, his parents had flown over from New Zealand to watch his debut.
He lasted 12 minutes. He didn't play again that 2008 season. For some time he wondered if he would ever play in the NRL again.
Moa was released by the Sharks at the end of 2008 and linked up with Hull FC to play in the UK Super League.
"The plan was to play for one year because I only signed a one-year deal but one turned into four," says Moa, who is in Liverpool with the Kiwis World Cup squad preparing for Monday morning's warmup game with the Cook Islands.
"I always planned to come back but I wan't playing well enough for any club to be interested in me.
"I knew I had a little bit of ability but I was too lazy. I had to change or I would have stayed there for the rest of my career."
Moa was so desperate to return to the NRL he almost offered to play for free. The Rabbitohs showed some interest but nothing eventuated. Then Manly sniffed around but they passed as well. Moa took rejection badly.
His luck changed through the help of Craig Fitzgibbon. The former Roosters, NSW and Australia back-rower played with Moa at Hull, and Moa tried to match the example Fitzgibbon set in training, but returned to Australia in 2012 to join the Roosters coaching staff.
Fitzgibbon persuaded new coach Trent Robinson to give Moa a chance, even though few had ever heard of him.
"It had got to a point where I was willing to come back [to the NRL] for nothing so I could prove myself," the 27-year-old said.
"Last year I was at home and had just had bicep surgery. I was offered a good deal to stay and was thinking I was going to have to spend the rest of my career in England when I got a call to say the Roosters were interested and prepared to offer a two-year deal.
"I think I said yes before my manager finished explaining the terms. I was over the moon.
"I didn't want to live in England any more. My partner was back in Australia because her visa had run out. I wanted to prove to myself that I had what it takes to play in the NRL and prove everyone else wrong. That was a big drive for me."
Moa not only proved he belonged in the NRL, but also stood out. In 23 games, he ran for an average of 97m and made 22 tackles. More than that, he was recognised as one of the strongest ball-runners in the competition.
The only lowpoint was when he was named as one of three Roosters players who returned elevated readings for HGH - there were no suggestions the trio acted improperly and they were cleared by both the NRL and the Australian Sports Anti-Doping Authority - but he took out his frustrations in being named against the Knights in the next game in the grand final qualifier.
"I have always tried to play as hard as I can because I'm not as big as the other front-rowers going around," says Moa, who is 1.83m and 105kg. "I have to make up for it with something different. My mentality is go hard or go home.
"I have always been a pretty hard runner but that was for only one or two hitups. Now I need to find the balance of being a lot fitter and being more consistent, punching out some more minutes."
His played a significant hand in helping the Roosters secure the NRL title and his form was also rewarded with a place in the Kiwis 24-man World Cup squad. It will be his second World Cup, after playing for Tonga in 2008, but as a former New Zealand under-16 representative and Junior Kiwi there was little doubt about switching allegiances.
"It was probably the best seven days of my life," he says about being named in the squad two days after playing in the grand final.
Certainly better than a few of days back in 2008.
