Australia's Matt Giteau expects New Zealand fly-half Daniel Carter to make an instant impact when he returns.

Carter has not played a Test since rupturing an Achilles tendon playing for Perpignan six months ago, but Giteau insists time out of the game would not have diminished his great rival's vast and silky array of skills.

The Giteau-Carter clash will have a huge bearing on a game Australia must win to stay alive in both Bledisloe and Tri-Nations calculations.

"I regard him as the best fly-half in world rugby so for me it's a huge challenge and one I'm looking forward to," Giteau said.

"I will be preparing as if he'll be in his top form. That's how I'm expecting it.

"If they pick him, he's fit and if he's fit he will be playing well.

"That's the way I will be approaching it - that he's in good form."

Asked how he viewed his own form heading into such an important match, Giteau replied: "As a side we're just that little bit off and individually I feel a bit the same.

"Training has gone well and I'm preparing well and once we get into some running rugby it will be good and I'm able to get more involved in the game.

"That's the biggest thing, just getting more involved."

New Zealand defeated Australia 22-16 in Auckland last month, continuing a worldwide trend of the home side prevailing.

The Wallabies upset the All Blacks in Sydney last year and second-rower Nathan Sharpe admitted playing on Australian soil was an advantage heading into Saturday night.

"I think it's consistent right across rugby in the world at the moment - home ground advantage is proving quite an enormous benefit and hopefully we can keep it that way this weekend," he said.

"Everyone's got that little bit of intensity about them and that's what you want to see going into these games."