The Wallabies will learn their Rugby World Cup quarter-final opponents on Sunday afternoon when Ireland play Italy in Dunedin.
If Ireland win, Australia will meet South Africa next Sunday, but an Italian victory will have the Wallabies facing Wales on Saturday.
"It appears most likely it will be South Africa," said coach Robbie Deans.
"They're building nicely and have shown they've got an ability to get up and the World Cup really suits their approach."
Argentina should cement their quarter-final place against New Zealand when they play Georgia in Palmerston North on Sunday afternoon.
England will meet France at Eden Park in Auckland next week.
Coach Martin Johnson said they would not be lulled into any sense of security by the French team's defeat by Tonga on Saturday. It was their second loss in pool matches.
France captain Thierry Dusautoir also warned England not to underestimate them.
"We've had two defeats from four matches. I think it will be the first time a team has qualified with two defeats (in the professional era)," said coach Marc Lievremont.
England beat France in the semi-finals at the last two World Cups.