Sonny Bill Williams has appealed against a World Rugby ruling that left him unavailable for New Zealand's Bledisloe Cup opener against Australia.

All Blacks centre Williams was given a four-week ban for a dangerous tackle on Anthony Watson during the second Test against the British and Irish Lions.

Williams has already served half of his suspension, sitting out the third Test against the Lions and Blues' last Super Rugby match of the season versus Sunwolves.

New Zealand Rugby felt the world champion's match of two halves against Taranaki and Counties Manukau should count as one of the four "meaningful matches" he must miss, as well as a Counties Manukau pre-season encounter.

A World Rugby judicial committee, however, ruled that the shortened games on 11 August involving Counties Manukau and Taranaki could not be recognised.

The governing body said Williams will not be free to play until 20 August, a day after the All Blacks take on the Wallabies in Sydney.

Cross-code powerhouse Williams has not given up hope of playing in that match, though, opting to challenge the ruling.