The 101-Test fly-half rolled his left ankle during a routine training drill on Tuesday afternoon and was assisted from the field in pain.
The 33-year-old admitted to being frustrated by the injury but insists he is not concerned, saying he has loose ligaments in his ankles and he experiences this type of ankle sprain regularly.
"I've got really loose ligaments in my ankles, if any ligaments at all, so I'm pretty prone to that happening and it's a minor injury as far as I'm concerned," he said.
Larkham will spend a couple of days recuperating and is confident of re-joining his team-mates at full-contact training later this week.
Larkham added that the Wallabies are focused on maintaining their momentum from their recent Tri Nations performances and are looking at Australia's pool match against Wales as their first real test.
"Our plan for the World Cup has been to basically play with our best side through the Tri Nations to get a little bit of combination and a little bit of confidence and I think we've done that and it's a matter of continuing that now through to the World Cup," said Larkham, who will move to Edinburgh after the tournament in France.
"You don't want to take too much away from the (opening) game against Japan but realistically the game against Wales is the biggest of the pool matches for us and we need to build for that."