Israel Folau insists he'll be right to face Wales on Saturday despite playing little role in the Australia's captain's run on Friday.

The superstar fullback was largely a spectator at Twickenham as his team-mates went about final preparations -- to the tune of AC/DC's Thunderstruck which was being belted out over the PA system -- for their Pool A decider at the Rugby World Cup. A win for either side will put them through to what appears to be the easier side of the knock-out draw in that it doesn't feature either New Zealand or South Africa.

Folau has barely trained this week after rolling an ankle in the first half of the Wallabies' 33-13 victory over England last weekend, but the former NRL star is adamant he'll be able to contribute against a team whom he has scored three tries in two Tests.

"It's not 100% but I'm confident otherwise I wouldn't be strapping on the boots and going out there," Folau said. "Everyone gets niggling injuries and you have to get through that as a player."

"If I wasn't right I wouldn't play. It wouldn't be fair on the team because you would go out and play half-heartedly. I had a couple of days off during the week to make sure everything was all right.

"I had a run around with the guys yesterday [Thursday] and it felt pretty good so I'm ready to go."

Australia's Israel Folau shows off his second straight John Eales Medal © Getty Images

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The two-time John Eales Medallist hasn't enjoyed the sort of impact at the tournament many had predicted, and even spilled a couple of high balls -- a mistake rarely seen in his three-year rugby tenure -- against England last week.

But some of his most breathtaking moments have come against Wales -- including an 80-metre interception try in the five-point win at Millennium Stadium last year -- while few can forget George North's 'reverse tackle' where he carried Folau on his shoulder, despite having the ball, during the second Test of the 2013 British & Irish Lions series.

While Folau has been a thorn in Wales' side in two matches at the Millennium, it's the form of Wallabies playmaker Bernard Foley that most concerns assistant coach Sean Edwards.

Foley scored 28 points against England last weekend in easily his best performance in the gold jersey and, crucially, kicked a perfect seven from seven to allay fears over the Wallabies' goal-kicking.

"Fly-halves are normally the pivotal position in a team," Edwards said. "I watched him through the Rugby Championship and I've admired his play for quite a while.

"He plays very flat and he's good at recognising the speed of the ball. If the ball's quick, he'll flatten up and that gives the defence less time to adjust.

"The width of the pass from nine helps him get a little bit wider. He was outstanding in the last game against England."