Australia backs coach Stephen Larkham revealed that full-back Israel Folau is unlikely to start against Wales at Twickenham on Saturday.
The Wallabies face Wales in a crucial fixture that decides the outcome of Pool A.
Should Australia win, they are likely to play Scotland in the quarter-finals, while a loss on Saturday will see them face up against South Africa, who only have to overcome the USA Eagles on Wednesday to top Pool B.
The superstar full-back injured his ankle during the convincing victory against England on Saturday.
"We have an injury concern over Israel," confirmed Larkham.
"He came off the field in the game against England with a sore ankle and did not train yesterday [Monday]. We will see how he pulls up today and I am not sure if he will even train."
Meanwhile, winger Rob Horne is also on the sidelines nursing a shoulder injury and is unlikely to make it on to the park at Twickenham.
"Rob is still on the injured list but we are hopeful he can be turned around in a week or so," added the former Brumbies pivot.
"It is unlikely he will face Wales."
The injuries in the backline leaves the door open for utility back Drew Mitchell and flyer Henry Speight to make their way into the matchday 23.