Stephen Larkham has been ruled out of the Australia side for today's pivotal World Cup clash with Wales in Cardiff after suffering a knee injury in training.

Larkham's fly-half position in the Wallabies side will be taken by rookie Berrick Barnes, who made his Test debut off the bench in last weekend's 91-3 win over Japan.

Larkham will undergo exploratory surgery in Montpellier on Monday that will determine whether or not his World Cup — and his Test career — are over as he has plans to retire after this tournament.

But Australia coach John Connolly is hopeful Larkham could be available for the Wallabies' final Pool B match against Canada on September 29th.