The Wallabies have suffered their third major setback within a week after Quade Cooper suffered a suspected ruptured Achilles.
Cooper picked up the injury during the 41-26 victory over Argentina in Mendoza, writhing in agony on the ground early in the second half.
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He was assisted from the field and took no further part, with SMH reporting he had suffered a rupture.
"The obstacles in the path becomes the path," Cooper said via social media after the game, seemingly confirming the news.
Rennie and the Wallabies must be left scratching their heads after yet another blow, with fellow overseas superstar Samu Kerevi ruled out for the rest of the year with a knee injury at the start of the week.
This comes as captain Michael Hooper was a late withdrawal due to personal reasons, with no timeframe put on his return.
The trio join Dave Porecki (concussion), Andrew Kellaway (hamstring), Angus Bell (toe), Scott Sio (neck/shoulder), Izaia Perese (patella) and Cadeyrn Neville (knee) on the sidelines after a brutal England series.
Cooper's setback tested the Wallabies depth, having gone into the match with a 6-2 forward split on the bench.
Reece Hodge slotted into the position with ease as he kicked Australia to victory, looming as a potential replacement alongside Noah Lolesio and James O'Connor.
“Geez, we’ve had a reasonable run of injuries haven’t we?” Rennie remarked to Stan Sport.
“What we know with Hodgey is he’s trained all over the place this week and we needed the other guys to step up. I thought we were far more clinical (in the second half), we applied a lot more pressure…really happy with how we finished,
“That’s the thing about this group, there’s a lot of character and courage and they stood up.
Cooper missed the England series with a calf complaint, ruled out of the first Test in the warm-up.
This allowed Lolesio to step into the role for the three-Test series and looms as the favourite to take over the role.
