Australia's women's Rugby World Cup hopes took a hit Monday with star sevens recruit Charlotte Caslick ruled out with an ankle injury.

The Olympic gold medallist and Sevens World Cup-winner switched to the 15-a-side game this year to fulfil her dream of playing at the tournament in England later this month.

She was named in Australia's squad last week despite the injury, but will now not travel.

"We're really disappointed to lose Charlotte so close to the World Cup," said Australia coach Jo Yapp.

"She has shown great commitment to the XVs program and Wallaroos this year."

Utility back Caslick, a three-time Olympian, had ankle surgery last month and was hoping to be fit, but will instead focus on her rehabilitation.

She was replaced by uncapped teenager Manua Moleka.

Australia, whose best World Cup result was third in 2010, begin their campaign against Samoa on August 23 in Salford.