New Zealand coach Steve Hansen wasn't happy with Scott Barrett's sending off. Photo: Jason Reed/Reuters

SYDNEY Lock Scott Barrett could miss the start of the World Cup after becoming only the fourth New Zealand international to be sent off during a test match in the 47-26 Rugby Championship loss to Australia in Perth on Saturday.

French referee Jerome Garces adjudged that Barrett had committed a dangerous tackle when he made contact with the head of Australia captain Michael Hooper with a no-arm tackle at a ruck just before half time in Perth.

The offence usually carries a six-week ban and Barrett will definitely miss the second Bledisloe Cup test against the Wallabies in Auckland next week, which the All Blacks must win to retain the trophy they have held since 2003.

It could also put him in doubt for New Zealand's World Cup opener against South Africa in Yokohama on Sept 21, another big blow after his fellow lock Brodie Retallick dislocated his shoulder in the 16-16 draw with the Springboks last week.

All Blacks coach Steve Hansen said the dismissal had been costly even if he was more concerned about how many tackles his side had missed.

"It's not good enough when first half you miss 10 or 20 tackles out of 90 so we were not going well," he said.

"We were starting to get into the game and then, lack of discipline, we get a guy sent off and it's not a team you want to play with 14 against.

"We were just starting to come right defensively, you can't miss first time tackles, it puts you on the back foot.

"In the end we missed a lot of tackles but that's because of the simple fact that we only had 14 guys on the park and the guys were trying to do three jobs rather than just their own."

Hansen said he had been encouraged by the spirit shown by his team despite playing with one man fewer for half of the match.

"At the end of the day, both sides were out on their feet, so all credit to Australia, good win," he added. "Having said that, I'm still proud of our boys, the way they stayed in there with 14 men, they didn't lie down."

With Hansen on the record as saying the Bledisloe Cup is the second most important trophy for the All Blacks after the World Cup, the Wallabies could face quite a backlash at Eden Park next week.

"Lots can change in seven days," Hansen said. "Attitudes change, we probably won't have Scotty Barrett so we'll have to make some team changes, but we've just got to get our game going and play with a bit more confidence."

Cyril Brownlie in 1924, Colin Meads in 1967 and Sonny Bill Williams two years ago were the other All Blacks dismissed in tests. Garces also showed Williams his red card for a shoulder charge during the second British and Irish Lions test. 

Reuters