Barrett announced details of his "sabbatical" with Top League side Suntory Sungoliath which will see him miss the Super Rugby season for the Blues but be availble for the 2021 international season.

A clause in the 29-year-old's four-year NZ Rugby contract was a lengthy break at the start of this year and a season in Japan.

"For me it made sense to go next year and then have two years back with the Blues and hopefully the All Blacks in the lead-up to the Rugby World Cup," said Barrett on Thursday.

"My wife and I are excited to head to Japan next year. It is an appealing place for a young family and comparatively safe in health terms.

Leading NZ Rugby official Chris Lendrum said Barrett's contact clause was similar to that of All Blacks locks Brodie Retallick and Sam Whitelock who played in Japan this year.

Whitelock returned from the aborted Japan season earlier this year while Retallick is playing two seasons there before resuming his New Zealand contract.

"That flexibility in our contracting is key: it allows our top players to refresh in a different rugby environment but remain committed to New Zealand Rugby which, in the long term, is great for both parties," Lendrum said.

The 84-Test veteran has been an influential figure for the unbeaten Blues through the first three rounds of Super Rugby Aotearoa, having played the previous nine seasons for the Hurricanes.

He said he had enjoyed the change of team and the tough nature of the Kiwi-only competition.

"I'm loving every minute of it and having such big crowds turning out has been fantastic," he said.

"It is an excellent environment with great coaching and an awesome bunch of dedicated players. While the excitement about heading to Japan will build closer to the time, I'll also be looking forward to being back later in 2021."

Suntory's coach is New Zealander Milton Haig while England coach Eddie Jones acts as a consultant for the club.

Australian Associated Press