New Zealand lock Scott Barrett has been suspended for three weeks following his red card in last week's heavy Bledisloe Cup defeat against Australia.

Barrett was sent off prior to half-time as the All Blacks suffered their join-heaviest loss – a 47-26 Rugby Championship defeat to the Wallabies in Perth on Saturday.

The 25-year-old was ordered off for a no-arms tackle on Michael Hooper at Optus Stadium, where world champions New Zealand conceded the most Test points in their history.

Barrett accepted a guilty plea on Tuesday, ruling him out of this week's second Bledisloe Cup clash with Australia in Auckland.

The ban will last up until September 1, meaning Barrett will be available for New Zealand's final Rugby World Cup warm-up against Tonga on September 7.

"Having conducted a detailed review of all the available evidence, including all camera angles and additional evidence, including submissions from his legal representative, Stephen Cottrell, the Foul Play Review Committee upheld the Red Card under Law 9.16," SANZAAR Foul Play Review Committee chairman Adam Casselden said.
 
"With respect to sanction the Foul Play Review Committee deemed the act of foul play merited a mid-range entry point of 6 weeks due to World Rugby instructions that dictate any incident of foul play which results in contact with the head and/or neck must start at a mid-range level. 

"However, taking into account mitigating factors including the Player's exemplary judicial record, his expressed remorse and the fact the Player has pleaded guilty at the first available opportunity, the Foul Play Review Committee reduced the suspension to 3 weeks."

"The Foul Play Review Committee adjourned the hearing to seek more evidence regarding the Player's proposed schedule of matches. Upon reconvening the Foul Play Review Committee was presented with extensive evidence demonstrating the Player's intended playing schedule."