Queensland's Cameron Munster and Murray Taulagi are in doubt for the State of Origin decider after returning positive rapid antigen tests.
Munster and Taulagi are isolating from their Maroons teammates as they await the results of PCR tests, which if positive, will rule them out of the match at Suncorp Stadium.
Brisbane winger Corey Oates will join the Maroons' squad as a possible replacement for Taulagi.
Munster has not played at club level for Melbourne since before State of Origin II in Perth, where he suffered a shoulder injury.
But he had been expected to return to fitness in time for the Origin decider.
If Munster is ruled out, Ben Hunt appears the likeliest option as a replacement in the Queensland halves alongside Daly Cherry-Evans, pushing Harry Grant into the starting side at hooker.
NSW Blues utility Nicho Hynes tested positive earlier in the week and was replaced in the extended squad by North Queensland's Chad Townsend.
Meanwhile, Steve Renouf expects Dane Gagai to flick Origin switch and rediscover his typical Queensland form for the decider.
The Maroons centre is under pressure ahead of Origin III after missing 18 tackles in the series.
Outplayed by NSW opposites Jack Wighton and then Matt Burton in Sydney and Perth respectively, Billy Slater has shown faith in the 21-game veteran to deliver with the series on the line.
Former Queensland centre Renouf can't see Gagai letting him down.
"That's Origin and that's the pressure of that arena but we've seen with Dane, he's been amazing at Origin level nearly all of his games," Renouf said.
"That was a hiccup and we won't see that again. He'll bounce back, he's too good a player and mentally he just loves that arena.
"They (NSW) went on that try-scoring spree in the second half, you won't see that from another Queensland team, especially up here at home."
A caveat to that guarantee could be that Billy Slater's forwards can't be beaten to the punch again, 13-game Origin great Renouf admitting his hands were sometimes tied as a centre outside a beaten pack.
"You can feel that as an outside back, the domination in the middle," he said.
"Unfortunately that has an effect on you; you go 'oh s***' ... get in there, try too hard do something because it gets to desperation stakes and the game's so quick. That happens.
"And that happens a lot at Origin level. In the 90s NSW had a fair forward pack and they dominated us in a lot of those games."
Despite NSW's forward pack dominance, Renouf said Slater was right to retain the side that lost in Perth, Tom Gilbert replacing Felise Kaufusi in the only change due to personal reasons.
"He's got to stick because that's what we pride ourselves on here, that's what we've built and why we've got to where we are," he said.
