South Africa utility back Adrian Jacobs is warning the Wallabies not to underestimate the hunger of a second-string Springboks side in Saturday's Tri Nations clash in Sydney.

The world champions have no fewer than 21 players ruled out through injury, including vice-captain Victor Matfield, hooker Bismarck du Plessis, five-eighth Butch James, lock Bakkies Botha and winger Bryan Habana.

Subsequently coach Peter de Villiers has named a largely untried squad for the 'Boks opening clashes with the Wallabies and New Zealand next week.

Despite being given little chance of success in their opening two matches by the media back home, Jacobs insists the lure of making the cut for this year's World Cup is a huge incentive for the players.

"We've got guys in the squad who have played Test rugby before and all of us are looking forward to playing and we want to show the world we didn't come over here to fool around. We're here to play rugby," Jacobs said on Monday.

"There are a lot of places in the side still open and the guys at home will know that many of this team can go to the World Cup and this is an opportunity for every player to show that they are good enough to wear the jersey."

The 30-year-old admits he is desperate to make it to the World Cup, which starts in New Zealand in September, and believes a strong start to the Tri Nations campaign against the Wallabies will hold him in good stead.

"I have played 30 Tests, but I have never gone to a World Cup and it is something to work on, and it's my dream to be involved in one," he said.

"I need to show that I can still make it. We have a lot of critics at home that don't think we can and it's up to us to prove that we are."

The Wallabies will go into the game against the Springboks reeling from Sunday's shock defeat to Samoa, but Jacobs believes little should be read into the result.

"It was a bit of a surprise for all of us, but Australia is a proud nation and, like all good teams, they will bounce back, hopefully not this week," he said.

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