Slater is satisfied outside back Selwyn Cobbo is back to full health after resting him from the game-two loss, but is remaining tight-lipped on David Fifita's chances of selection for July 17.
Queensland's bench hooker Grant was rested from Melbourne's first game after the Marons were thrashed 38-18 in game two, but it has since come to light he is contending with a sternum injury.
The Storm also sat Grant out of Saturday night's 40-28 defeat of Wests Tigers, though football boss Frank Ponissi attributed that decision to "bumps and bruises" his captain is carrying.
But despite the lack of game-time, Slater has not yet put a line through his former teammate as he contemplates tweaks to his beaten bunch for the series finale at Suncorp Stadium.
"(Grant) hasn't been ruled out," Slater told The Sunday Footy Show.
"He's had a couple of weeks off now, he didn't play the game after the Origin, he sat out the game on the weekend.
Queensland's Harry Grant remains a chance for State of Origin's game three. (Dave Hunt/AAP PHOTOS)
"I know Harry pretty well, I've been speaking to him over the last couple of weeks. He's in a pretty good place."
Slater is willing to put similar faith in Newcastle fullback Kalyn Ponga, who will take the field for the first time in 11 weeks during Sunday's clash against Canberra.
Seven-time Maroon Ponga missed last year's series to recover from a serious concussion and is unlikely to displace Reece Walsh from the fullback spot.
But after shaking off a foot injury, Ponga is considered a leading contender for the bench utility role that Cobbo filled to acclaim in game one.
"The first thing I'm looking at for Kalyn is hopefully he goes out there and he's got a big smile on his face. He's missed a whole heap of footy," Slater said.
"He's playing this afternoon for the Knights and we'll go from there. But look, he's been a big part of the Queensland team for a number of years, missed last year and was in great form at the start of the year.
"He's just got to get back on the field and start playing footy."
Slater said Cobbo was "certainly one of the candidates" to replace the injured Xavier Coates in the Maroons' backline after the Brisbane flyer missed Origin II amid niggling injuries.
"(He's) back playing, nice and fit now and performed well," Slater said, impressed with Cobbo's performance in Friday's loss to Penrith.
But Slater was coy on Fifita, the Gold Coast wrecking ball overlooked for the first two games of the series despite excellent individual form this season.
Fifita could add muscle to a Maroons bench that struggled in the game-two loss, but Slater said he would not speculate on Fifita's chances given two games were yet to be played on Sunday.
"It would be disrespectful to throw names out there and say this guy's in the team, this guy isn't," he said.
Slater insisted the injured Latrell Mitchell's withdrawal from the NSW team would not influence his own selections after opposite man Valentine Holmes struggled to curb the left centre's influence in Origin II.
"It's pretty dangerous if you start selecting your team on what the opposition are going to do," Slater said.
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