NSW are "very confident" in Ethan Strange's troublesome ankle after clearing the Canberra playmaker to feature in the State of Origin decider.

The Blues had set Monday as D-Day for Strange, who has been fighting to prove his fitness since rolling his left ankle at training on Thursday.

Strange, excellent on debut in the series opener, had undergone extensive treatment and been walking unassisted in NSW camp in recent days.

He managed to run at training at Ballymore Stadium in Brisbane on Monday, staying late to complete extra contact work and running drills. 

The Blues had initially been pessimistic about Strange's hopes of playing the decider. The 21-year-old had rolled the same ankle against Wests Tigers in April and needed a week out to recover.

But Stange was always confident he would retain his spot for Wednesday night, when the Origin shield goes on the line at Suncorp Stadium.

"(It's) great news, especially where he was a couple of days ago, where he was probably more unlikely than likely to play," said Blues football manager Frank Ponissi.

"He ticked every box. He's relieved ... his confidence the last few days has probably made us confident as well.

"We wanted to be certain this morning, and after that session, we're very confident."

Matt Burton had been on stand-by to replace Strange, but returns to Sydney to continue preparations for Canterbury's NRL clash with Canberra.

It's yet another close brush for Burton, who has earned three Origin caps but been selected as an unused 18th player an additional five times.

"Any time I get the call to come in here, whether's it's a back-up or 18th man, I'll definitely put my hand up," Burton said.

"I love just coming in here and representing NSW.

"I was just here to fill in and help the boys prepare as best as I could. Hopefully I did that, looking forward to seeing how they go."

News of Strange's recovery is a welcome boost for NSW, who lost Mitch Moses and Casey McLean to injuries in the days ahead of games one and two, respectively.

Strange was close to the Blues' best player replacing the injured Moses as NSW pulled off the greatest comeback in Origin history to win game one.

"The medical team have done a wonderful job," Ponissi said.

"We saw what he could do in game one, so to have him available on the bench is a big asset for the team."

Strange may not be deployed from the six-man bench on Wednesday, but will be relied upon in the event of an injury to either of the starting halves in Nathan Cleary and Moses.

Strange came on for a late cameo in the Blues' game-two loss.

Blues teammates had always been privately hopeful Strange would be fine to play.

"The ankle, I'm not a doctor but I've had a couple of them, they're pretty easy to strap and that sort of thing," said Blues prop Mitch Barnett.

"I think it's a bit different if you're going a hamstring or soft-tissue sort of thing, but he just rolled his ankle."