McLean will have scans on Thursday but already knows the injury won't allow him to play in the decider against Queensland in Brisbane next Wednesday.
The news is devastating for the 30-year-old, who was set to become the sixth-oldest Blues' debutant in State of Origin history after being named by coach Brad Fittler as the replacement for the injured Payne Haas.
McLean, whose career has been blighted by several serious injuries, said he knew as soon as he tested the injury at Thursday's training session he was out.
"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," McLean said through tears.
"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."
The Blues are yet to confirm a replacement but Newcastle's Jacob Saifiti, who trained with the Blues on Wednesday before returning to the Knights, is set to make an immediate return to the camp.
Parramatta's Reagan Campbell-Gillard, who played in game one, is another option.
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.
Hynes, who was with the squad in Sydney earlier this week after being named as a reserve by Fittler, didn't travel to their northern NSW camp.
The Cronulla half instead stayed in Sydney to prepare for the NRL match between the Sharks and Melbourne.
He returned a positive RAT test prior to the Sharks' training session on Wednesday and a subsequent PCR test also came back positive, meaning Hynes will miss Thursday's game as well as next week's Origin III.
Townsend was subsequently added to the squad presumably to fill the role of 19th man and is unlikely to play unless injury or illness forces Fittler into a reshuffle.
But the 31-year-old was a notable absentee from Thursday's training session at the Cudgen Leagues Club.
The North Queensland captain is instead spending his first full day at camp in his hotel room as he deals with a bout of gastro which team officials described as "mild".
Townsend has tested negative for COVID-19 however 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, was back training as the Blues ramp up their preparations to win a series decider in Brisbane for just the third time in Origin history.
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