Wallabies captain Stirling Mortlock has been ruled out for the remainder of the Tri Nations series with a knee injury.

Mortlock was forced from the field during Australia's 29-17 loss to the South Africa in Cape Town on Saturday.

The mercurial outside-centre underwent scans in Sydney on Tuesday where fears were confirmed the 32-year-old had suffered a lateral cartilage tear, which requires surgery.

Mortlock will undergo the procedure on Wednesday and is expected to be sidelined for six weeks.

Australia have lost their opening two Tri Nations clashes and are languishing last on the ladder with just one bonus point.

With Mortlock out for Australia's four remaining Tri-Nations matches, coach Robbie Deans is likely to move Adam Ashley-Cooper to No.13, with youngster James O'Connor expected to slot into fullback for the Test against the All Blacks in Sydney on Saturday week.

Utility forward Peter Kimlin is also expected to be out of action for up to six weeks with a shoulder injury which was sustained on the recent Brumbies development tour of Europe.

Deans has called for reinforcements with Brumbies lock Mark Chisholm and NSW Waratahs back Kurtley Beale being added to the Wallabies Tri Nations squad when it reassembles in Sydney on Thursday.

Chisholm played his comeback match for Sydney club side Randwick last weekend after having been sidelined since early April with a broken wrist.

Beale is yet to play for the Wallabies.

Deans on Monday said he would disclose the identity of the replacement captain for the August 22 game when the team was announced.

Flanker George Smith, who has captained Australia before, is among the leading candidates for the job.

Brought to you by AAP © 2024 AAP