The Wallabies will be without captain Michael Hooper for tomorrow morning's Test against Argentina, after the skipper informed coach Dave Rennie he's struggling mentally.
The four-time John Eales Medallist told team officials on Thursday night his "mindset" is not where it should be to lead the team against the Pumas on Sunday morning (AEST).
In a statement, the Wallabies said: "The 121-Test openside flanker believes he's not in the mindset to fulfil the responsibility that goes with leading and representing his country at this point in time."
James Slipper will take over the Wallabies captaincy, and Fraser McReight will come into the team at No.7.
Hooper said: "While this decision did not come easily I know it is the right one for me and the team at this point in time. 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."
The Wallabies are supportive of the 121-Test skipper and have given him the green light to take as much time as he needs.
Rennie will address the media on Saturday morning (AEST) and described Hooper's decision as courageous.
"Michael's one of the most professional and impressive men I've coached (and) I know this has been a difficult decision for him," Rennie said in a statement.
"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."