The Wallabies might need outside reinforcement for Sydney's decisive third Test against England after a likely serious knee injury for Izaia Perese headlined the carnage in Brisbane.
Scans will confirm if the utility back tore his ACL in Saturday night's 25-17 loss at Suncorp Stadium.
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Lock Cadeyrn Neville also suffered a knee injury, fullback Jordan Petaia was concussed in the third minute and Scott Sio (arm, shoulder) lasted no longer when he came on in the second half.
Allan Alaalatoa (concussion) and centre Len Ikitau (calf) should both be fit to play at the SCG on Saturday at least.
But with Jed Holloway, Quade Cooper, Tom Banks and Andrew Kellaway already in the casualty ward and Darcy Swain suspended for another Test the cupboard is almost bare.
The Wallabies remain particularly thin in the second row and at fullback, with Reece Hodge flown into the squad as cover and now a potential fix in the No.15 and Nick Frost a chance to start after debuting off the bench.
Rennie said he'd consider added a second-rower to the squad once a clearer picture of their injury toll was possible on Sunday.
It paves the way for code-hopper Suliasi Vunivalu's much-hyped debut on a wing or off the bench, the former NRL premiership winner training strongly with the squad after a series of hamstring injuries since returning to rugby.
Petaia's early exit was a headache for a side searching for a fullback ahead of next year's World Cup, Kellaway strong when moved there in Perth but now facing up to eight weeks on the sideline.
Petaia stumbled to his feet after a tackle gone wrong and would appear long odds to feature in Sydney in another setback for the talented 22-year-old.
Rennie won't use the injuries as an excuse though, given his team came from 19-0 down to threaten an upset in Brisbane.
"We lost the collisions early, they choked us down our end but the first time we got down we scored seven," he said.
"When we played territory we put them under heat and at 22-17 we had all the momentum and a lineout (was lost because of a bad throw) and they were able to swing the length of the field and get three points."
Australia scored two tries to one but Owen Farrell's six penalties and a conversion from eight attempts was the difference.
"We knew it (the physicality) was coming, we just didn't tackle well enough ... and we have to look at our discipline," Rennie said.
