Facing their biggest challenge at the Rugby World Cup, the Wallabies will have to overcome the loss of Israel Folau and David Pocock against a Scotland outfit buoyed by the surprise availability of two of their stars.
The quarter-final clash at Twickenham on Sunday (Monday 0200 AEDT) is, coach Michael Cheika insists, their toughest encounter to date despite successfully escaping the "Group of Death" with victories over England and Wales - both ranked higher than the world No.9 Scotland.
Crucially, the Wallabies will need to win the elimination clash without the tournament's form player, Pocock, and their most dynamic back, Folau.
Cheika said the decision was taken out of his hands as Pocock failed to train at all during the week due to his calf injury, while Folau broke down at training on Friday despite appearing to have overcome his ankle complaint.
"They couldn't do their jobs and that's the key," Cheika said on Sunday.
"You've got to be able to do your jobs in this team and I don't think either player could do it to their full potential."
They've been replaced by Kurtley Beale and Ben McCalman, both in impressive form themselves, and Cheika is confident there will be minimal disruption.
"It's really just a straight swap for those guys," Cheika said.
"We'll just ask them to improve the team with what they bring.
"I know Pocock and Folau are great players but I really believe in the guys who are coming into their positions.
"All the guys that are coming in played significant roles during the Rugby Championship and then the Test in America and the lead up games."
They will be playing for the right to face either Ireland or Argentina in next week's semi-final.
Scotland received an enormous boost on match eve with the news that hooker Ross Ford and lock Jonny Gray successfully appealed their tournament-ending suspensions for a two-man tip tackle on Samoa's Jack Lam.
The surprise result means the influential duo will be free to face the Wallabies, and has been hailed as a win for commonsense by South African great Francois Pienaar.
"I thought (the ban) was harsh and I'm glad they did rescind it," said Pienaar.
"It's hugely important that they play for Scotland. They were outstanding (against Samoa). The pack just played beautiful rugby."
The match will feature veteran pair Stephen Moore and Matt Giteau in their 100th Tests, and they will become the seventh and eighth Wallabies to achieve the mark.
Meanwhile, winger Adam Ashley-Cooper plays his 112th in the gold jersey - overtaking George Smith to become the third-most capped Wallaby, trailing only George Gregan (139) and Nathan Sharpe (116).
