Wallabies skipper Michael Hooper has withdrawn from Australia's tour of Argentina for personal reasons.
Rugby Australia released a statement saying Hooper, 30, would return to Australia.
The Wallabies kick off their Rugby Championship campaign against Los Pumas in Mendoza on Sunday morning (AEST).
The statement said the 121-Test veteran is "not in the mindset to fulfil the responsibility that goes with leading and representing his country at this point in time".
"While this decision did not come easily I know it is the right one for me and the team at this point in time," Hooper said.
"My whole career I've looked to put the team first and I don't feel I am able to fulfil my responsibilities at the moment in my current mindset."
Experienced prop James Slipper will captain the side in Hooper's stead in Mendoza, with Reds flanker Fraser McReight stepping in at open side.
Wallabies coach Dave Rennie said his skipper had shown "true courage" to make the "difficult decision" to step aside.
"Michael's one of the most professional and impressive men I've coached," Rennie said.
"He's shown true courage by acknowledging where he is at and acting on it.
"We will support him in any way we can and I know the team will be focused on getting the job done."
Rugby Australia boss Andy Marinos described Hooper as an "incredible leader" while pledging the organisation's ongoing support.
"It takes a brave man to identify where he’s at and come forward whilst having the best interests of the team at heart,” Marinos said.
“His wellbeing is and remains the highest priority right now."
Hooper has been a stalwart of the Wallabies since 2012 and has been full-time captain since 2015.
He is the Wallabies' most capped skipper of all time.
The Wallabies enter this year's Rugby Championship off the back of a 2-1 series defeat against England.
In last year's competition the Wallabies finished second behind the All Blacks.[ABC sport newsletter