Front-rower Greg Holmes will miss Australia's tour of Europe next month after failing to recover from a neck injury sustained in training.
Holmes has returned to Brisbane for scans on the injury
The Wallabies 2006 rookie of the year will be replaced by ACT Brumbies prop Nic Henderson.
Team officials said Holmes was unable to participate in any scrum sessions during the first two days of the Wallabies' four-day camp in Sydney.
"It's extremely disappointing but it is still very sore," said Holmes.
Australia are already without rested skipper George Gregan and his fellow scrum-half Sam Cordingley, who was forced to pull out with a persistent foot injury.
Cordingley's place on the tour goes to NSW Warratahs scrum-half Josh Valentine.
Coach John Connolly has said Matt Giteau is likely to be tried at scrum-half on the tour.
Giteau has established himself as a centre or fly-half for the Wallabies but started his career as a scrum-half and is set to get his chance earlier than anticipated after Cordingley's injury.
"We had targeted him to play there later in the tour anyway but we'll probably have a look at him earlier rather than later," said Connolly, who added it was a possibility Giteau could start against Wales on 4 November.
The Wallabies line up against Wales, Italy, Ireland and Scotland from 1 November.
1 Nov - Ospreys v Australia A, Swansea
4 Nov - Wales v Australia, Cardiff
11 Nov - Italy v Australia, Rome
15 Nov - Ireland A v Australia A, Limerick
19 Nov - Ireland v Australia, Dublin
21 Nov - Scotland A v Australia A, Perth
25 Nov - Scotland v Australia, Edinburgh