Australia's Rugby World Cup plans are in disarray after scans revealed game-breaking winger Digby Ioane has a fractured thumb that requires surgery.

The fact that the Wallabies have not called for a replacement despite such an injury usually taking four to six weeks to mend is an indication of how important Ioane is to Australia's cause.

Apart from being arguably the most potent attacking winger in the world, Ioane's defence is integral to the Wallabies' entire game plan.

Ioane defends in the midfield channel, allowing five-eighth Quade Cooper to drop back to fullback - not only to trigger counterattacks but also to protect Australia's influential playmaker from the frontline defence.

While coach Robbie Deans and fellow selectors David Nucifora and Jim Williams are spoilt for options, given Australia's embarrassment of backline riches, deciding on a replacement for Saturday's Pool C crunch match with Ireland is bound to stress the Wallabies' brains trust.

Deans' two most obvious options are:

- promoting Drew Mitchell, Australia's leading tryscorer at the 2007 World Cup, as a direct swap for Ioane on the left wing;

- recalling first-choice goalkicker James O'Connor, who was outstanding off the bench in Sunday's 32-6 win over Italy, but play him on the left wing instead of his preferred right flank.

The second scenario would hand a reprieve to Anthony Faingaa, who looked under the most pressure to retain his starting spot after making way for O'Connor's introduction against Italy.

Deans could also play Mitchell and O'Connor on the wings and move 'Mr Fix-it' Adam Ashley-Cooper to outside centre - or even give the classy Rob Horne a crack at No.13.

Whatever Deans and company decide, the burning question remains: Who will defend in Cooper's midfield channel?

Ioane suffered the fracture with about 20 minutes of play remaining when he accidentally came into contact with the boot of his Italian counterpart Mirco Bergamasco as he attempted to cover a grubber kick in behind the Australian line.

As Ioane tried to scoop up the ball, his thumb was struck by the boot of Bergamasco, who was attempting to toe the ball further down field.

Australia's leading scorer during the Tri Nations tournament - who scored one five-pointer and made a great break to set up another in Sunday's impressive win - will apparently undergo surgery in New Zealand.

Post-surgery, Ioane will remain in camp with the Wallabies in the hope he can return for the knockout stages of the tournament, although the exact timelines for a comeback will not be known until after the joint has been repaired and his rehabilitation has begun.

Should the Wallabies decide Ioane's injury isn't progressing well enough for him to make a return, they are permitted to replace the 26-year-old.

But under IRB rules, once replaced, a player cannot return to the tournament.

NSW Waratahs winger Lachie Turner would seem the most logical choice of player on standby for Ioane.

Australia's clash with Ireland is likely to decide the winners of Pool C, with the losers almost certain to be pitted into a dreaded sudden-death quarter-final against the defending champion Springboks.

The victors at Eden Park on Saturday will probably be left to face Wales or Samoa in the sudden-death stages.

"Obviously this will be a grand final game for us," Wallabies fullback Kurtley Beale told AAP.

"These Irish guys are very passionate. When they get a roll on, they're unstoppable, so it's very important to go out there and stop that."

Ioane, many bookmakers' favourite to top the tournament's tryscoring tally before being injured, said he remained hopeful of returning to help the Wallabies win the Cup.

"Just been blessed by a priest at the hotel!," he tweeted fans on Monday night.

"Now can't wait for the surgery an thanks heaps 4 the support my friends:)"

Brought to you by AAP © 2024 AAP