After fighting their way through the so-called group of death with England and Wales, then surviving a heart-stopping quarter-final against Scotland, the Wallabies are battling a high-injury list and fatigue as they prepare for Sunday's semi-final against Argentina.
The players were given a rare day off on Thursday to rest their bodies before Cheika announces his team on Friday, with even the top leaders unsure if they will be picked.
Matt Giteau, who earned his 100th cap against the Scots last week and was named man of the match after the 35-34 thriller, said the competition for places was good for everyone.
"No-one knows who's playing. The competition is tough, training is very game-like and as soon as you get that combativeness and a training environment like that you're only going to get better," he said.
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"We've got so many great players in the backline but also in the forwards as well so everyone is pushing everyone for positions.
"Everyone wants to play and everyone seems to be playing well so it's a tough job I think for the selectors."
Blindside flanker Scott Tardy said everyone in the squad had shown they were capable of stepping up. Number eight David Pocock missed the match against Scotland because of injury and was replaced by Ben McCalman.
Kurtley Beale filled in for Israel Folau at fullback and Drew Mitchell played on the wing for the absent Rob Horne.
"I've said it a number of times in the tournament, that we're very confident in the backrow depth that we have got. But we've got that in a number of positions," Fardy said.
Giteau said the mood within the Australian camp was positive. "As a team, we're committed to one goal and everyone's buying into it," he said.
"Even the guys that don't get a lot of game time have been superb around the group. That just speaks volumes about the environment that's been created by the coaches but also the one that's been created by the leaders as well.
"We're getting addicted to the process of trying to get better and just staying tight as a group."
Off the field, the Wallaby coaching staff have all played key roles.
Former Argentina hooker Mario Ledesma has done wonders with the Australian scrum since being appointed forwards coach while Steve Larkham, a World Cup winner for Australia in 1999, has been helping the backline.
Giteau was a team mate of Larkham's during the 2003 World Cup, where Australia finished runner-up, and said his advice was proving invaluable as they prepare for the semi-finals.
"I think as far as our structure and plays and dissecting the opposition is concerned, he's very smart. Even when he played he was good," Giteau said.
"He used to be very quiet as a player but as a coach he speaks a lot, gets his messages across well."
(Reporting by Julian Linden; editing by Martyn Herman)
