The Wallabies suffered a major blow ahead of their Tri Nations/Bledisloe Cup clash against the All Blacks on Saturday night.

Captain Stirling Mortlock has been ruled out for this weekend's match in Sydney.

The inspirational skipper has failed to recover sufficiently from the head knock he sustained in the second half of last weekend's 16-9 Tri Nations victory over South Africa.

Western Force centre Ryan Cross will start the match at outside centre in his captain's absence.

Mortlock's departure led to flanker George Smith assuming the captaincy.

The Wallabies/All Blacks match will kick off on Saturday at 10pm.