Wallabies halfback Will Genia will undergo surgery after allegedly being "king-hit" early in their Test against Ireland.
In a massive blow for the Australians' hopes of winning the series in the third Test in Sydney, Genia is out until at least the Rugby Championship starting in August.
He stayed on the sidelines but coach Michael Cheika revealed the break at the post-match press conference.
"He's broken his arm so he will be going for surgery tomorrow," Cheika said.
The coach said Genia was taken out off the ball as the Australians ran a decoy play.
"We ran the play round the front and Will is the decoy around the back and he got king-hit from the side, it looked like a shoulder, and when you're not expecting it that's what happened," Cheika said.
"I'm not sure who it was but they jammed his arm and broke it."
Genia will miss the Melbourne Rebels' push for a maiden Super Rugby finals berth, with his team taking on the Waratahs in a top of the Australian table clash on June 29.
Genia only had one match back - last Saturday's opening-Test win in Brisbane - after missing a month with a knee injury.
The third Test will be played next weekend in Sydney.