Barnett had the worst news confirmed on Monday in Auckland, after being assisted from Accor Stadium in the Warriors' 36-30 win over South Sydney on Sunday.
His injury comes as a mega blow for the Warriors, with Barnett a key member of the club's rise up the ladder to second spot this year.
It is also a significant issue for the Blues.
Barnett laid an early foundation for NSW in their 18-6 series-opening win, and has just two-and-a-half weeks before the next clash in Perth on June 18.
Stefano Utoikamanu looms as the favourite for the spot, after he was part of NSW's 20-man squad for game one and placed on standby for Payne Haas.
But Keaon Koloamatangi will also likely remain an option, after being the form prop of the NRL for the past month following his move infield from the second row.
The Rabbitohs forward topped 200 metres again against the Warriors, scored a try, made eight tackle busts and played 80 minutes for the third straight game.
Koloamatangi debuted in the 2023 dead rubber, starting in the second row and tapping on a pass in the lead up to the first NSW try.
"Obviously one of my big goals is to get back there," Koloamatangi said.
"But obviously you've got to play good at club level to be able to make the team. So I'm trying to just do that."
Asked if he would enter the arena better prepared now with that experience under his belt, the Souths enforcer said he would.
"Especially after playing for Tonga against Australia as well," added the 27-year-old.
"They're obviously a mixture of both New South Wales and Queensland players.
"My confidence is high at the moment. I feel like I'm playing good footy. Whatever happens, happens."
Koloamatangi's move to the front row has made him one of several big-minute machines in the middle.
Haas has long been the benchmark for props, while Terrell May has also become an 80-minute option for Wests Tigers after his move there from the Sydney Roosters this year.
Koloamatagi's situation is slightly different, given he lost 10kg in the pre-season - which made him the leanest he has been since he was a teenager playing centre.
"You've got to be lean and a lot fitter than back in the day. There's not many big-muscle props anymore that play," Koloamatangi said.
"Especially with the interchanges going down to eight. The more minutes you play, the more valuable.
"No matter what position I play, I try and be the best at it.
"Obviously, the best props in the world, like Payne, they play massive minutes and do a massive amount of work. So I just try and do that for my team."
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