Ben McCalman will miss the third Test and up to six weeks of rugby with a fractured scapula.
McCalman, who came off the bench in the second Test, hurt his shoulder blade in his first involvement of the game, coach Michael Cheika said.
The backrower played out the rest of the game, with no replacement on the bench.
Cheika said it was disappointing that McCalman didn't have a chance to push his starting credentials.
"He didn't really get a chance to do what he does... he's proven for us over the time I've been involved that he's a serious campaigner," he said.
"He would've been a chance (to start this week) but I wasn't unhappy with the back row last week.
"There was a few basic errors but I thought they worked hard."
Leroy Houston will join up with the squad in Sydney to replace McCalman.
McCalman will likely be the only forced change to the Wallabies side for the final Test, though Cheika flagged some other potential reshuffles.
"We'll probably make a couple of changes," he said.
"I thought I might make a couple each game just to have a look at guys who have shown either through Super Rugby or through the series [that] they're vying for spots.
"We'll sort those [changes] out over the next day or so."
