But the returning Wallabies prop has declared himself 100 per cent fit for what he has dubbed the contest for rugby's Olympic Games gold medal.

Sio has made a remarkable recovery from an injury that could have ruined his World Cup campaign and put him through months of pain and rehabilitation.

The front-rower was left in agony when a scrum collapsed on his right arm in Australia's tense quarter-final win against Scotland.

He immediately knew something was wrong, but it wasn't until Wallabies doctor Mike Cadogan told him he would need to "pop" his elbow back in place that Sio realised how serious it was.

"It was in the scrum … we sort of all collapsed and I didn't have time to let go of Stephen Moore and I dislocated my elbow," Sio said.

"They tell me I'm lucky because I'm pretty young, mobile and didn't break anything. It was unfortunate, it goes like that sometimes in rugby. I'm lucky it wasn't too major.

"I tried to walk it off but knew I'd done something pretty bad. The doc was good, he kept me calm and popped it back in. The elbow is easier to put back in [than a shoulder]."

Sio has vowed not to let his teammates down when he makes his return in the biggest game of his rising career.

He said he would not have made himself available if he felt unable to handle the heat of a World Cup final.

"Things like this, you've just got to be pretty honest with yourself and honest with the team," Sio said.

"[Missing the semi-final] was a bitter pill to swallow. But at the end of the day, could I bind that scrum, could I stay in the maul and could I get guys up in the lineout?

"If I'm not able to function 100 per cent then there's no point putting yourself out there."

The Wallabies' scrum struggled in Sio's absence against Argentina, giving away four penalties – the most in any of Australia's games at the World Cup.

But Sio knows the Wallabies face a huge challenge against an experienced New Zealand pack that is ready to claim back-to-back world titles.

Sio has his World Cup inspiration sitting in the stands, with dad David watching on 24 years after he played for Samoa in a historic quarter-final against Scotland.

David named his son Scott because Samoa lost that match to Scotland.

Twelve years ago David gave up his ticket to the Wallabies' World Cup final against England in Sydney so son Scott could go along and watch.

Sio still remembers lining up for autographs from George Gregan, Stephen Larkham, Lote Tuqiri and George Smith.

"It's crazy that 24 years ago I was being born during a World Cup and now I'm playing in the Rugby World Cup final," Sio said.

"It's amazing having my family here, who I hold closest to my heart. They're the reason I play this game.

"The biggest advice my dad has told me is to not get lost in the rugby. You forget what's around you.

"Back in 2003 I was just a young kid going up to the likes of George Gregan, Stephen Larkham, Lote Tuqiri and asking them for their autograph. I'm in this position now, so it's about never forgetting it. Always cherish it."