De Villiers has already lost centre Frans Steyn from his plans due to a tournament-ending shoulder injury on the same day that a serious groin problem sidelined New Zealand superstar Dan Carter.
And having had to overcome second-row injury troubles earlier in the tournament, De Villiers will keep fingers crossed for no further setbacks.
"We are worried about our two wingers at the moment," he said.
"But I think this long week will give us sufficient time for them to get back on the field."
South Africa have arrived in the last eight by emerging unbeaten through the tournament's toughest pool, defeating Wales, Fiji, Namibia and Samoa.
Australia, in contrast, have had their problems, suffering regular injury setbacks and being knocked out of their stride by Ireland's stirring victory over them earlier in the competition.
But De Villiers added: "Their decision-making is really spot on, and then when they get turnovers they are really better than most teams in that they come from depth and they make yardage immediately.
"They force the width and they force the space around the field quite well.
"If they get it right, you are in for a long, long day. If you can shut it down, for them it's going to be a nice and equal contest."
Springboks skipper John Smit said: "This is the stage where every game is do or die.
"It's a different level completely, and you can feel the shift wherever you go in terms of how important these play-offs are going to be.
"We will see which teams can use their individual experience of playing in play-off rugby to the best of their ability, making sure that you take in the heat as much as possible and yet remain composed in terms of what you want to achieve.
"Game-plans will differ according to the opposition you're playing and according to the weather conditions you've got.
"There are going to be so many factors that come into play, and I think we are fortunate that we do have a few guys who've seen a few scenarios played out before in the last decade.
"Pressure is what makes the game beautiful and what creates some special performances. Without those I don't think you ever quite reach the top of the game.
"We haven't beaten them (Australia) this year, and last year wasn't fantastic either, so they are a team that have had one up on us for the last two seasons."
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