Australia's injury and illness woes are bordering on crisis, with the Wallabies barely having the numbers for a match-day 22 to take on the USA on Friday night.

While the Wallabies are playing down the situation the mathematics is plain and simple.

Coach Robbie Deans and fellow selectors Jim Williams and David Nucifora only had two players - third-string halfback Nick Phipps and prop Salesi Ma'afu - considered but not picked this week.

With wingers Digby Ioane (thumb) and James O'Connor (hamstring), flankers David Pocock (back) and Scott Higginbotham (back) and hooker Saia Faingaa (flu) all sidelined and lock and captain James Horwill needing to rest a battered shoulder, Deans said it was "a pretty straightforward team to pick to be honest".

"It's easy because you only pick those who are fit and able," he said.

Deans is hopeful all but Ioane, who is confident of returning for the quarter-finals after requiring surgery, will be available for Australia's final pool game on Saturday week against Russia.

He put on a brave face in front of cameras, saying injuries were part and parcel of rugby.

"They're always a concern. You could do without them, but they're a constant as well," Deans said.

Pocock has now been sidelined for two successive games, O'Connor has a grade one hamstring strain and doctors have assured Deans that Higginbotham's back complaint - suffered at training on Wednesday after he'd been picked to start - should ease in days, not weeks.

An MRI scan has already cleared Horwill of any structural damage, while Faingaa, like Higginbotham, was also scratched on Wednesday after being named on the bench.

"Saia's ill. We didn't want that running through the group, so we sent him back to bed," Deans said.

Rocky Elsom, initially chosen on the bench after a draining seven-Test campaign, was promoted to replace Higginbotham, with Stephen Moore, who missed the weekend loss to Ireland with a gastric illness, the new reserve hooker.

So impressive off the bench this year for the Wallabies, Higginbotham can't take a trick.

"Scotty was named this morning but, at training, had a back issue and he's withdrawn," Deans said.

"We'd warmed up and, first event, he experienced discomfort and left the pitch.

"It wasn't a matter of excessive aggression or anything."

Halfback Will Genia will captain the team, which features six changes to the starting side that lost to Ireland.

Rob Horne will play his first Test in more than a year when he lines up at inside centre, while Drew Mitchell starts on the wing in O'Connor's place.

There are four changes to the starting forward pack that was badly outplayed by the Irish.

No.8 Wycliff Palu replaces Radike Samo in the back row alongside Elsom and Ben McCalman, who retains the openside flanker role with Pocock still out but said to be improving.

Veteran Nathan Sharpe and youngster Rob Simmons take over in the second row from Horwill and Dan Vickerman.

James Slipper comes in at loosehead prop in place of Sekope Kepu, joining tighthead Ben Alexander and hooker Tatafu Polota-Nau.

Australia: Kurtley Beale, Adam Ashley-Cooper, Anthony Faingaa, Rob Horne, Drew Mitchell, Quade Cooper, Will Genia (capt), Wycliff Palu, Ben McCalman, Rocky Elsom, Nathan Sharpe, Rob Simmons, Ben Alexander, Tatafu Polota-Nau, James Slipper. Res: Stephen Moore, Sekope Kepu, Dan Vickerman, Radike Samo, Luke Burgess, Berrick Barnes, Pat McCabe.

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