Australia captain Stirling Mortlock's Tri-Nations campaign remains in serious doubt with the veteran set to undergo scans on his injured left knee tomorrow morning to determine his immediate playing future.

Mortlock, who was replaced in the 30th minute of his side's 29-17 loss to South Africa at Newlands on Saturday, limped into Sydney airport on Monday without the aid of crutches.

And while hopeful he has not played his last Test of the tournament, the skipper was far from confident when asked to assess the severity of his injury.

"You know in yourself when it doesn't feel right and it didn't feel right so we'll investigate - it's really hard to tell, you don't know with these things so fingers crossed," he said.

"All things being considered it's not too bad at this stage.

"We'll get scans either this afternoon or tomorrow and then know exactly what's in front of us."

Coach Robbie Deans admitted he was not expecting Mortlock's scans to reveal good news, conceding the 32-year-old is facing the very real prospect of missing the Wallabies' four remaining Tri-Nations fixtures.

"Stirling will need an MRI (scan), he had an x-ray and there's no bone damage but there's still the prospect of some cartilage damage," Deans said.

"And if that's the case then he'll need a clean-up which would probably rule him out potentially for the remainder of the Tri Nations."

While Mortlock's absence would be a massive blow, the captain strongly rejected suggestions the Wallabies' Tri-Nations campaign is as good as over following consecutive losses.

"Every home team has won their matches, there's been no bonus points secured either, I think we're the only ones who've secured a bonus point by losing within that (seven-point) margin so the Tri-Nations is wide open," he said.

"Obviously we've got a lot of work in front of us but it's (the competition) very tough."

The Wallabies will reassemble in Sydney on Thursday to begin preparations for their must-win clash against the All Blacks at ANZ Stadium on August 22nd.