The Wallabies have suffered a major setback ahead of Saturday's rugby championship decider against the All Blacks in Sydney.
Lock Rob Simmons has been ruled out of the match with a wrist injury which requires surgery, and he will also miss next week's Bledisloe Cup Test in Auckland.
However he Simmons was expected to make a full recovery before the Wallabies play the United States in Chicago in the lead-up to the World Cup starting next month in England and Wales.
Simmons, a veteran of 52 Tests, has been Australia's lineout caller and leading jumper, so coach Michael Cheika will be forced to carefully weigh his options before selecting his locks to face the World Cup holders.
Cheika has the choice of two veterans in former skipper James Horwill and Dean Mumm to replace Simmons, and could also drop non-jumping giant lock Will Skelton to start both of them in the second row.
After struggling for form this year, Horwill impressed when he came off the bench in last month's Test win over South Africa in Brisbane.
Recently returned from an overseas stint, Mumm was just as impressive off the bench in the victory against Argentina in Mendoza a week ago.
"Obviously we're all disappointed to lose Rob," said Cheika.
"We've been able to build some real depth in the lock position, and Rob's injury presents an opportunity for another player in the squad to stake their claim."