Australian rugby's dire lack of playmaking depth was rudely exposed with 100kg skipper Stirling Mortlock unveiled as the Wallabies' back-up five-eighth.

The desperate Wallabies will hope and pray nothing should ground Matt Giteau on Saturday night as their Tri-Nations hopes would certainly unravel without the star No.10 against New Zealand.

Mortlock ran in the pivotal role for the first time at training at Ballymore where even sickness to inspirational flanker Rocky Elsom was of less concern to onlookers.

The Wallabies skipper will make a rare start at inside centre due to the scratching of multi-talented Berrick Barnes (shoulder) which has left the 22 without a proven second ball-player.

Instead of calling in an internationally-unproven youngster such as Quade Cooper or James O'Connor to provide cover, coach Robbie Deans showed his hand, slotting Mortlock in the unlikely position one off the ruck in training.

An outside centre who started his 71-Test career on the wing, Mortlock's ball-playing ability was even the butt of light-hearted jokes from his former long-time centre partner, Giteau.

"This year I think that Stirling has learnt to pass so he can play inside centre and outside centre, he's been going very well," he jibed before going into bat for the captain.

"I think he'd like to do it (play No.10). He had a run today at five-eighth and went very well. I think the team went better with him there so he'll take a lot out of that."

But as much self-depreciation Giteau could muster about his own training form, the NZ coaching staff wouldn't risk such a big Test without having their own recognised back-up playmaker to cover for maestro Dan Carter.

"I'm not sure I would," said All Blacks assistant coach Wayne Smith. "It is a pivotal position but I know Rob well over a number of years and he'll have a back-up five-eighth, there's no doubt about that.

When told the left-field back-up was Mortlock and then asked what he could bring to the role, he didn't have to think long: "Gain line. He'll run at anyone".

"They've had a kicking option there with Berrick Barnes (at No.12) and I'm not sure if Stirling gives them that but he's a great player."

With the likes of Mortlock and similarly-sized Ryan Cross in the midfield, Giteau expects to have a target on his back in defence.

"I generally think most teams would be targeting me, myself or Berrick, when we've both been 10 and 12, so I don't think this will be any different," he said.

"It's a Test match and I won't be going out there in a dinner suit. If you are going out there you have to make your tackles.

"With the big centres we've got you'd think a lot of the traffic would be going my way.

"Vice-versa, they've got big centres and back-rowers as well so there's going to be a bit of traffic going down Dan's way as well."

Smith rated Giteau with Carter as the best No.10s in the world and denied NZ viewed him as a potential weakness - but they would be testing him in both defence and attack.

"You want him to be busy and you want him to be making decisions but he's not a target," he said.

In just his first full season of five-eighth, Giteau admitted he was still growing into the role after producing both good and bad in a topsy-turvy Tri-Nations campaign.

"I feel a lot more comfortable each week and each game is a big learning curve for me," he said. "I still feel I'm learning a lot in games, even the one we got flogged (53-8) in Johannesburg."

The All Blacks will on Friday finalise their line-up with reserve prop John Afoa to have his injured shoulder tested more fully in training.

Neemia Tialata is on stand-by.

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