Genia heard three cracks in his right knee when he landed awkwardly with 11 minutes remaining in Australia's 26-19 win over South Africa and knew his fate almost immediately.
"I'm gutted," said Genia.
"I took the high ball and as I landed I twisted in on my knee and I got hit and then it twisted further.
"I knew I'd done something as soon as I heard the cracks and then when I got up and tried to take off and couldn't support any weight I knew I'd done something quite serious."
The Wallabies say they're up to the character test that will come with losing a player as influential as Genia.
The Queensland star said he'd help 23-year-old Phipps through what will be just his second start and fourth cap for the Wallabies.
Genia is confident there's enough experience in the group to cope without a third elected skipper.
"Sharpie assumes that leadership role and what last night and over the last couple of weeks has showed is we're building depth," he said.
"I reckon (Phipps) will do really well. He's got a good work ethic and he's got a big motor."
Deans, who has received some relief from the pressure mounting on his job, said the tenacious game of Sheehan will benefit the group and is confident Phipps will cope despite his lack of Test experience.
"Phippsy's ready. It's been a challenge for him to be in the shadow ... but he's understood the need for him to really immerse himself in training as though it's the game," said Deans.
Lock Sitaleki Timani (hamstring) is highly unlikely for the Argentina fixture, with Rob Simmons or Kane Douglas to replace him.
Veteran hooker Stephen Moore succumbed to a low grade hamstring injury before the Springboks match, while centre Rob Horne tore his hamstring in club rugby.
The positives for the Wallabies are that inside centre Pat McCabe is available for selection against the Pumas and James O'Connor will join the squad with a view to being fit for the trip to South Africa and Argentina later this month.
Winger Drew Mitchell has also managed to avoid needing further surgery on his troublesome leg injury and will return to full training.
-AAP