Barnes, one of three contenders for the fly-half position along with the mercurial Kurtley Beale and strong kicker Mike Harris, has also appeared at inside centre this year as well as full-back.
"I'm sure I'll either be at 10 or 15, and if I'm full-back then I'll have a lot more work under the high ball. No side tests the full-back as much as the Springboks do. People talk about the forward battle, but you have to deal with the kicking game as well," Barnes said.
Barnes is fully expecting the Springboks to bombard the Wallabies with high kicks and said the tactic had contributed to Australia struggling to beat them in Perth on September 8.
"You're not allowed to kick in Australia!" he joked. "But there's a real appreciation for the kicking game here, I guess it depends on what you find entertaining.
"It's a huge part of test rugby, how you exit your own half and we struggled with that in Perth. We'll endeavour not to try as many grubbers this time.
"They can be effective if you get them through the line, it's just we didn't get any through.
If Barnes does play at flyhalf, he is expecting the Springboks to put pressure on him by running at his channel with their big centres.
"Frans Steyn is over 100 kilograms, he's not small, but you have to deal with it as best you can, much like tackling Ma'a Nonu or Sonny Bill Williams," he said.
"It's not an easy task and I'm sure they'll use that same channel to attack, although you also have to be aware of what's outside that with Bryan Habana and Jean de Villiers, who hasn't been getting many raps but he's one of the best centres in the world."
Wallabies media manager Matt McIllraith said a gastrointestinal bug had affected the Australian camp, with lock and captain Nathan Sharpe, props James Slipper and Ben Alexander, lock Sitaleki Timani and loose forwards Liam Gill and Scott Higginbotham all being laid low.
The Wallabies are also waiting on the fitness of hooker Stephen Moore, who strained a hamstring. McIllraith said uncapped Queensland Reds hooker James Hanson was on his way to South Africa to cover for Moore.
If the 29-year-old does not play on Saturday, he will remain level with Jeremy Paul on 72 caps as Australia's most-capped hooker.
The Wallabies will announce their team on Thursday afternoon.