Australia captain Michael Hooper has withdrawn from Saturday's Rugby Championship opener away to Argentina and will return home as he is not in the right "mindset" to play.
Rugby Australia said Hooper had informed the team of his decision.
Wallabies coach Dave Rennie said Hooper had "shown true courage".
"While this decision did not come easily I know it is the right one for me and the team at this point in time," said Hooper, 30.
"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."
Prop James Slipper will lead the side in Mendoza with Fraser McReight replacing Hooper as flanker.
Hooper, who made his Wallabies debut in 2012 and has won 121 caps, last year passed George Gregan's record for most Tests as captain.
Rennie said: "Michael's one of the most professional and impressive men I've coached - I know this has been a difficult decision for him.
"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 tomorrow [Saturday]."
Rugby Australia chief executive Andy Marinos added: "Michael is an incredible leader, it takes a brave man to identify where he's at and come forward while having the best interests of the team at heart.
"His wellbeing is and remains the highest priority right now where Rugby Australia and the Australian Rugby community will do everything to support him and his family."