Michael Cheika said he had all but settled on his side for the first pool match against Fiji on September 23 (Thursday, September 24 1.45am AEST).

Palu's absence opens the door for Cheika to employ a double openside flanker act with Michael Hooper and David Pocock.

The Wallabies are being cautious with hard-hitting back-rower Palu as they test combinations in the first two pool matches before taking on England and Wales. "Cliffy has had a bit of a hamstring [problem], but he ran [on Tuesday] which was good," Cheika said.

"He probably won't be right for the first game, but he will probably be right for the second game. [Hooper and Pocock] are still a possibility, we've got a good idea. After the [Rugby Championships] we sat down and worked out what we thought would be our teams.

"We'll let that play out, we're in a good situation. We're putting some bits together."

Hooper and Pocock haven't played in the same team since the Wallabies beat New Zealand in the opening Bledisloe Cup match in Sydney. The specialist No.7s loom as a key weapon for the Wallabies in their bid for World Cup glory.

Cheika is set to play two completely different starting sides in the first two matches against Fiji and Uruguay to find the best combinations.

There are just three days between the Wallabies' first two games and the unusual tactic of mass changes will give Cheika a chance to avoid over-working players and finding the best line-up.

Those teams are likely to be divided up in the coming days for opposed training sessions to start working on their combinations.

Cheika implemented an attacking mindset at the NSW Waratahs designed to win back fans and play entertaining rugby.

But he admitted the Wallabies need to find a balance between attack and tactical play in a tournament which was decided by a try-less final in 2007.

"You've got to play a little bit differently because you're playing against the best defences," Cheika said. "You won't win many matches without scoring tries, either.

"We've tried to get a few basic things right until now … we've still got some improvement we can make during the tournament.

"We've got a strategy we've planned out according to our opponents, we'll monitor that. We've gone into a different cycle of training now."

Skipper Stephen Moore said the Wallabies' two-week stint allowed the team to fly under the radar," Moore said.

"We know now that we're no longer in the building or preparation phase, we're in game mode and it's all very real. The pressure is on right from the start."