Skipper Stirling Mortlock has stormed to Timana Tahu's defence, claiming the under-fire convert played "exceptionally" in the Wallabies' last-start shocker in Johannesburg.

Tahu admitted he produced a terrible starting debut in the record 53-8 loss to South Africa, exposed at inside centre where he made poor defensive reads and missed tackles.

The former NSW Origin and Australian league winger even mused he was looking for a rope to hang himself midway during the Springboks' eight-try rout.

But with comments that throw a cloud over expectations that Tahu will be axed ahead of Saturday' night's Tri-Nations decider in Brisbane, Mortlock lavished praise on the novice.

"I thought Timana went exceptionally considering it was his first start in 12 at this level," Mortlock said.

"From my perspective all the negative press that's been out there has not just been of him but of the team.

"You take that on the chin but in particularly for him in his first start.

"He's a great player and he's going to be a great for us and him along with everyone in the team that experienced that loss will be better for it."

Wallabies coach Robbie Deans is facing a tough decision on who to play at inside centre against the All Blacks with preferred choice Berrick Barnes racing the clock with a shoulder injury.

Barnes believes he's 50-50 at best but Deans appears pessimistic about the low-tackling Queenslander's chances.

He must train solidly at Ballymore to prove he'll be close to 100 per cent fit for the crunch match, where Australia will attempt to end a seven-year Tri-Nations drought.

If Barnes is out, Mortlock looms as the likely No.12, moving one position in and another code-jumper, Ryan Cross, promoted to start at outside centre.

Cross hasn't disappointed in his first international season and also scored two second-half tries when he came off the bench to partner Mortlock in the centres at Suncorp Stadium against France in June.

Apart from Barnes, reserve hooker Adam Freier (hamstring) is the only other Wallabies squad member listed with an injury concern after he missed his Sydney club semi-final.

Freier, in the mix for a bench spot, will want to run freely at training to be selected ahead of Tatafu Polota-Nau on Tuesday.

Stephen Moore is a certainty to start at rake as one of six possible changes, due to his superior set-piece skills after the Australian scrum and lineout were dreadful in Johannesburg.

Flanker George Smith will start ahead of Phil Waugh while changes are also being considered at prop, second-row and fullback.

Seasoned lock Nathan Sharpe, eying a return after being dumped following the 39-10 loss to New Zealand on August 3, will arrive in camp after his wife gave birth to a son, Franklin, on Friday.

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