Australia prop Scott Sio insists he is fully fit as he prepares to return from injury in Saturday's Rugby World Cup final against New Zealand.

Sio missed the Wallabies' semi-final win over Argentina due to a dislocated elbow, but he replaces James Slipper in the only change to Michael Cheika's line-up for the decider.

The 24-year-old said he had no doubts over his fitness ahead of the final at Twickenham.

"I feel good, I’m 100 per cent confident in my elbow," Sio told a news conference.

"Yesterday was going to be the marker and I got through training really well, through all the scrums, mauls and the lineouts.

"Part of this process is being honest with yourself and honest with the team. I was honest. I said it felt really good and if they wanted to pick me for this week, I’d be ready for the challenge."

"There's no risk. You’ve got to go into this knowing you are 100 per cent ready for this occasion.

"It’s the biggest game rugby has to offer. You want to be part of it but it’s a team sport and you have to make sure you’re not putting the team at risk. I didn’t feel that and I told them I’m good to go."

Sio said he knew leading up to the semi-final, which Australia won 29-15 against the Pumas, that he was not ready.

"I was there or thereabouts [to face Argentina] but I knew I wouldn’t be able to give my all and I wouldn’t want to put the team in that position," he said.

"I made the call early in the week that I wasn’t going to be good to go.

"It was a hard pill to swallow because it was a semi-final. But to be given that chance again, in a World Cup final, I’ll definitely relish it now.

"I call the World Cup the Olympics of rugby. To be there at the pinnacle, at the end, is amazing."