Western Force full-back Cameron Shepherd is the front-runner to replace injured utility man Mark Gerrard in Australia's 30-man World Cup squad after the rookie was ruled out with a serious knee injury.

Young guns Lachie Turner and Digby Ioane are also in the mix along with rugby league converts Ryan Cross and Clinton Schifcofske.

``We'll pick the best person who I think fits in,'' Wallabies head coach John Connolly said.

Connolly insisted he would reserve his judgement until as later tomorrow as he weighs up a number of options.

The coach will sift through footage from recent Australian Rugby Championship matches to evaluate each player's form, while an injury to starting winger Adam Ashley-Cooper may also influence his decision.

``We'll take a couple of days to think about it...but more than likely we'll go with experience,'' Connolly said.

``And I guess having the advantage of being in the team, say in Cameron Shepherd's case, is an advantage for him.''

With Ashley-Cooper having been given less than a 50% chance of lining up against the Welsh at Millennium Stadium on Saturday, the Wallabies could be forced in a different direction.

``Obviously if we pick someone to cover like with like, we'll pick someone who can play wing and full-back because (Scott) Staniforth covers 12 for us, and Adam Ashley-Cooper covers 13,'' Connolly said.

``What confuses it a little bit is if Adam is out for an extended period of time, because he was the first cover at (number) 13.

``Indications are that he's a chance for Wales but more likely than not to miss it and that's why we're holding it (the decision) for another day or so just to confirm where Adam is at.''

Gerrard has been ruled out of the tournament after suffering a ruptured medial ligament in his left knee with his first touch in the World Cup against Japan on Saturday.

Gerrard's initial concerns were confirmed 24 hours after the match, leaving his campaign in tatters.

But he was quick to look on the bright side, saying: ``I've just got to get better from it and hopefully get better as a person and better as a rugby player.

``I'm only 25, (as of) about four days ago, but with that obviously hopefully I'll get another chance to play a World Cup and play more than a minute - two minutes would be better than one but life goes on.

``It's disappointing that I'm leaving the tournament after a minute, or not even a minute, but I'm very proud I've been able to pull on that gold jersey in a World Cup, even if it was for a minute.''

Connolly described the Wallabies' opening performance against Japan as ``satisfactory'' but is expecting a tough assignment against Wales in Saturday's Pool B clash in front of a full house in Cardiff.

``The home side in rugby has a huge advantage and if you look back over the last 10 years of rugby the team playing at home - Australia for example - great at home but struggle away,'' Connolly said.

The Wallabies' replacement player will link up with the squad on Thursday but is unlikely to win selection in the 22-man-squad for Saturday's pivotal clash with the Welsh.