An inquiry has found that Sonny Bill Williams should have been removed from the field in the first half of last weekend's Bledisloe Cup test against Australia in Sydney.

Rugby Championship governing body Sanzaar has admitted the All Blacks midfielder, who will start against the Wallabies in Dunedin on Saturday, showed obvious signs of concussion - a loss of balance after a collision - which should have resulted in his replacement with no head injury assessment.

A Sanzaar inquiry has found that there was no deliberate mismanagement involved, and that all parties would be reminded of their responsibilities to safeguard player welfare.

In a statement, Sanzaar said the review, which involved match-day and team medical staff determined:

•The incident was not identified during the game via the appointed HIA specialist, the match day doctor, the team doctors or the match officials 
•The available post-game video confirms ataxia, which would trigger immediate and permanent removal under World Rugby protocols 
•While no process is entirely failsafe, the review panel determined that the missed HIA incident should have been identified during the match

Sanzaar chief executive Andy Marinos said: "This is an unfortunate set of circumstances given the acute focus and attention we are all applying to player safety and in particular the HIA protocols. NZ Rugby has been proactive in its management of Sonny Bill Williams and we have full confidence in its processes to manage his return to play - as NZR has illustrated with other players such as Dane Coles and Ben Smith this year already.

"As a consequence, and even though there was no deliberate failure apparent, Sanzaar has taken the opportunity to strongly reinforce World Rugby HIA protocols including video analysis during the game, to all teams, match day medical staff and match officials participating in the Rugby Championship.

"Additionally, New Zealand Rugby has confirmed that Sonny Bill Williams is being managed in line with World Rugby HIA protocols, including HIA 3 and computer neuro-cognitive assessment, and will progress to a graduated return to play if asymptomatic," added Marinos.