Wallabies captain Michael Hooper withdraws on eve of opening Argentina Test

Captain Michael Hooper has withdrawn from the Wallabies' Rugby Championship Test against Argentina 24 hours before kick-off, saying he isn't in the right "mindset" to lead or represent the country.

The tireless flanker had been named to lead the side in his 122nd Test on Sunday morning (AEST) but will now fly home to Australia, missing both matches against the Pumas.

"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 in a statement.

"My whole career I've looked to put the team first and I don't feel I am able to fulfill my responsibilities at the moment in my current mindset."

Wallabies coach Dave Rennie said there were no signs through the week of Hooper's anguish.

"Nothing that was evident to us in how he trained, how he contributed around the team, around leadership was excellent but clearly he's been struggling a bit and masking that pretty well," Rennie told reporters from Argentina on Saturday (AEST).

"Obviously he's been able to suppress things over the past handful of weeks and so we certainly weren't aware of anything but he's such a professional and he was able to get on and do the job.

"He addressed the team today which took an enormous amount of courage to let them know that he's not OK and that he felt it was best for himself and for the team that he gets home.

"It was an easy decision to let him go home where he will get plenty of support around him."

Hooper reached out to the Wallabies team doctor Sharron Flahive, who put the wheels in motion for his return home.

He will travel back to Sydney with his Waratahs teammate Dave Porecki, who is unavailable for both Tests due to a training head knock.

Fellow Test centurion James Slipper will captain the side in Mendoza, while Fraser McReight will replace Hooper in the number seven jersey.

Rennie said that McReight was match-ready after recently playing in the Australia A Pacific Cup series.

"He's had three 80-minute performances so conditioning-wise it's not an issue.

"They use the same structures as us and he has been in our group in the past and so he'll fit seamlessly."

Hooper captained Australia during their recent 2-1 series loss to England at home and has been a regular presence in the side since making his debut in 2012.

The Wallabies, who have a World Cup in France next year, return to Australia for Rugby Championship Tests against South Africa and New Zealand beginning later this month.

Rennie said 30-year-old Hooper hadn't given any indication regarding his playing future and they didn't have a timeline for a return to action.