Australia captain James Horwill has been ruled out of Saturday's Rugby Championship clash against South Africa with a hamstring injury.
The 28-year-old tweaked his left hamstring at training on Tuesday and will miss his side's next two matches against the Springboks and Argentina.
Scrum-half Will Genia will captain the side in Horwill's absence for the fourth time in his career, while Waratahs lock Kane Douglas will be promoted to the starting side and Ben McCalman added to the bench.
It will be Douglas' first Test run-on appearance under coach Ewen McKenzie, having started all three Tests against the British and Irish Lions under former boss Robbie Deans.
The last time Genia captained his country he led the Wallabies to a 26-19 victory over South Africa in Perth 12 months ago.
"Will is a proven leader and has had plenty of success as captain for the Queensland Reds and also for Australia," McKenzie said.
"He is a player that thrives with the added responsibility and he has always stepped up when given the opportunity to lead. I'm sure this will bring the best out of him.
"It's extremely disappointing to lose James but after discussions with medical staff we felt it was important not to risk further injury when he isn't ready.
"Scans revealed his injury was on the lower-end in terms of severity and we expect him to be back to full fitness when we embark on our two-game tour of South Africa and Argentina in a few weeks."