Manly hooker Matt Ballin is poised to make his State of Origin debut in Sydney on Wednesday after Cameron Smith pulled the pin on his brave bid to play.

Smith, who has been receiving intensive physio for a dislocated elbow, underwent a private fitness test with former Origin player Jason Hetherington early on Saturday afternoon.

He was the first to deliver the news to his room mate Ballin who at first thought he was joking.

"I did everything I could to get there," said Smith, who has played the last 19 Origins in a row.

"Unfortunately the tests I had to do today, which included making some tackles, I couldn't get through that.

"Obviously I've lost a bit of strength in the arm. Everything straight at me was fine but when I had to stretch and reach out, it was not good.

"I knew straight away. I still had four days but it wasn't worth the risk."

Smith said Ballin was an ideal replacement.

"He's really excited. I told him when I got back to the room after the test and I don't think he believed me at first," said Smith.

"He was more apologetic that I was out.

"I asked him if anyone had spoken to him and I said: `I'm out mate, and you're in'."

"He's tough enough, he's a robust guy and he plays a lot of minutes for Manly."

Ballin, 26, from Kingaroy, is likely to start at hooker ahead of Cooper Cronk who will also get some time at dummy half.

Team physio Scott Thornton said Smith had been "close" to playing.

"Cam was pretty close but we put some time frames in place that he had to be able to do some defensive work by today and he just couldn't quite do it, so we had to make the call," Thornton told AAP.

"He did some tackling and he didn't feel comfortable with it, he didn't quite have all his strength so we weren't prepared to take the risk.

"It was a joint decision."

Smith, who suffered a dislocated elbow in the Test match against New Zealand on May 7, was always going to struggle to play in the first Origin game.

Ballin has been in camp with the Maroons since Tuesday and has taken part in every training session to prepare him for his debut.

The decision was made early to give him time to get used to the dummy half job which involves calling many of the plays for halves Darren Lockyer and Jonathan Thurston.

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