Australia's snaring of Kiwi Dave Rennie to coach the Wallabies for the next four years has further frayed the quality of contenders to replace All Blacks mentor Steve Hansen.

What began as a deep contest - NZ Rugby sounded out 26 applicants for their interest - has devolved into a two-horse race between Ian Foster and Scott Robertson.

Hansen's long-time assistant Foster hasn't been a head coach for eight years while successful Crusaders coach Robertson has no international or offshore coaching experience on his CV.

Among those known to have been approached are heavyweight candidates such as Rennie, Jamie Joseph and Warren Gatland, who have all landed international jobs elsewhere.

Joseph has extended his Japan head role for a further four years while long-serving former Wales coach Gatland was unveiled in June as coach of the British and Irish Lions in 2021, effectively putting his stated All Blacks goal on hold.

Critics in New Zealand believe NZ Rugby blundered by not beginning its search earlier this year, when it would have had a full field of contenders to choose from.

Commentators have opined that coaches wanting to cement their future beyond 2019 would have been reluctant to roll the dice on a highly contestable pre-Christmas All Blacks process.

For example, Rennie has been negotiating with Rugby Australia for six months and said New Zealand's interest came too late after being unveiled in the Wallabies role on Wednesday.

Prominent Kiwi rugby writer Gregor Paul said NZR was misguided to assert that appointing Hansen's successor well before the Rugby World Cup would have been a distraction for the All Blacks.

"New Zealand Rugby now has a PR disaster on its hands as the narrative since has been dominated by big names ruling themselves out," Paul wrote in the New Zealand Herald.

"It's fast becoming the job no one really wants and in an age of unprecedented coaching riches, it's embarrassing how many of the best candidates have actively said no to even applying.

"The job clearly doesn't hold the allure NZR thinks it does."

New Zealanders are the most sought-after international coaches and fears are increasing that their intellectual property will erode the All Blacks' world-leading status of the last decade.

Long-standing Highlanders chief executive Roger Clark said losing Rennie, Joseph and Japan assistant coach Tony Brown offshore would eventually have an impact.

"I'm biased as an All Blacks fan - I think it's pretty disappointing," Clark told Radio Sport.

"It is a body blow. We can't afford to be losing coaches of the level of those three that we've just lost in the last week to our environment."

"We've seen that the international market is insatiable in grabbing those guys away from us."

Australian Associated Press