Coach Robbie Deans must sort through the wreckage and identify 22 fit and able bodies capable of outclassing the USA as the Wallabies walk the Rugby World Cup finals tightrope on Friday night.

Of Australia's 30-man squad in New Zealand, only 22 were able to complete full training duties on Monday due to the bruising weekend loss to Ireland and a nasty virus that swept through the camp.

Already reduced to five weeks of sudden-death football, the Wallabies breathed a big sigh of relief after an MRI scan cleared skipper James Horwill of a shoulder injury that would have further undermined Australia's flagging campaign.

But Horwill, lock Dan Vickerman, centre Pat McCabe and winger James O'Connor were all too sore to train, while flanker David Pocock only managed some light run-throughs as he continues to battle the back discomfort that sidelined him from the Ireland encounter.

Recovering hooker Stephen Moore, another match-day scratching with a stomach bug, and ailing centre Anthony Faingaa, who was too sick to travel to Wellington on Sunday with teammates, also sat out the session.

Although star winger Digby Ioane (broken thumb) is the only squad member definitely unavailable for selection this week, Deans and selectors Jim Williams and David Nucifora still have an arduous job deciding on a starting XV and seven-man bench.

With no room for further slip-ups, it is a delicate balancing act for the Wallabies' brains trust.

Deans needs to give his travelling reserves, including Drew Mitchell, Rob Horne, Berrick Barnes, Luke Burgess, Wycliff Palu, Scott Higginbotham and Nathan Sharpe, some game time in case they're required for major roles later in the tournament.

But messing too much with a largely settled combination that secured the Tri Nations title and beat Italy in Australia's opening pool game before falling to Ireland is fraught with danger.

The USA are no mugs, as they showed in a hard-fought 22-10 loss to Ireland and subsequent defeat of Russia.

"They're a very passionate side," said Wallabies hooker Tatafu Polota-Nau.

"Just looking at a few clips, they can definitely upset sides by playing the general game rather than the set piece.

"Saturday was definitely a wake-up and any side (we play) would get a lift from that result."

With Faingaa ill and McCabe due a rest after starting in all seven of Australia's Tests this year, Deans must be tempted to reunite the formidable backline that accounted for the All Blacks in Hong Kong last October.

That would involve drafting in Barnes to start at inside centre, partnering Adam Ashley-Cooper in the midfield, and giving the Wallabies a second tactical kicker alongside five-eighth Quade Cooper, something they sorely missed against Ireland.

With Ashley-Cooper moving to outside centre, Drew Mitchell is in line for a recall to the left wing.

Securing victory over the USA with most of his backline big guns on deck would allow Deans to rest attacking generals Cooper and halfback Will Genia from Australia's final pool game against lowly Russia in Nelson.

Picking a forward pack is less straightforward, due to the uncertainty surrounding Pocock and Australia's generally poor back-row and scrum showing against Ireland.

If Pocock is again out, selectors have no alternative than to retain Ben McCalman at openside flanker because they didn't bring a specialist No.7 back-up to the tournament.

But reserve back-rowers Palu and Higginbotham need time on the park, as do second-rowers Sharpe and Rob Simmons, who may well get their chance if Horwill and Vickerman need more time to recover.

Scrummaging specialist Salesi Ma'afu is pushing hard for a start in the front row, especially after Australia conceded five penalties for repeatedly collapsing the set piece at Eden Park.

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