The North Queensland front-rower was poised to become the Blues' sixth-oldest debutant in Origin history in next week's decider against Queensland in Brisbane after being named as the replacement for injured Payne Haas.

It was an opportunity the 30-year-old thought had passed him by after narrowly missing out on Blues' selection in 2017 before a move to the Cowboys from Melbourne which has been dominated by injury and form issues.

McLean's past experience with hamstring issues left him in no doubt he wouldn't be fit for next week's game after suffering the injury and he ruled himself out even before undergoing scans.

"I don't really know what to say to be honest. It's pretty disappointing," McLean said, fighting back tears.

"My career has been full of ups and downs and I've kind of gotten used to it but I thought I might be at a bit of a light at the end of the tunnel getting this opportunity, but it wasn't to be."

"I still haven't talked to the family yet so that's going to be the hardest thing, telling them I won't be playing this week."

NSW coach Brad Fittler was shattered for McLean, who has made eight Test appearances for Australia but is yet to represent his state.

"He just has a history with these (hamstring injuries) so it's just heartbreaking the fact he doesn't get to play," Fittler said.

"Speaking to him, he feels like it's not a huge injury where he's going to be out for a long time.

"I'm always very conscious (of) trying to send the players back fit and healthy but for this one I'm just gutted he's not playing."

McLean's withdrawal left the Blues scrambling to bring Jacob Saifiti back into their camp at the northern NSW beachside town of Kingscliff.

The Newcastle forward had trained with the Blues on Wednesday before travelling to link up with the Knights ahead of Friday's NRL match against South Sydney.

Instead of featuring in that game however, Saifiti will now fly back to rejoin the Blues for what will also be his Origin debut.

"Every time the door closes, another one opens, so there's a good chance it'll be Jacob Saifiti," Fittler said.

"He was in our first camp and has been part of this camp as well."

Saifiti is the identical twin of Daniel Saifiti, who has made seven appearances for the Blues, and Fittler believes the 26-year-old is ready to step out of the shadow of his brother.

"He deserves it, he's had a good year," Fittler said.

"He was Newcastle's player of the year last year and the stuff we look at, he does very well."

Meanwhile, a day after being called into NSW's extended squad, playmaker Chad Townsend has been laid low by a bout of gastroenteritis.

Townsend joined the Blues' camp in Kingscliff on Wednesday after Nicho Hynes tested positive to COVID-19.

Unlikely to play given he's replacing Hynes in the No.19 jersey, Townsend has tested negative for COVID-19 and is expected to link up with the Blues squad after he's recovered.

Centre Matt Burton, who sat out Wednesday's session with a calf niggle, trained on Thursday to ease fears he's a doubt as NSW look to win a series decider in Brisbane for just the third time in Origin history.

Australian Associated Press