Ian Foster behind Ardie Savea's decision to sit out Bledisloe I

All Blacks coach Ian Foster has backed forward Ardie Savea's decision not to travel to Australia for New Zealand's upcoming Rugby Championship clash with the Wallabies in Melbourne, ahead of the birth of his third child.

Savea has been one of the All Blacks' most consistent performers despite the team's faltering form but has chosen to remain at home for his side's penultimate game in the southern hemisphere championship.

"He's a key leader, a key player, but I'm massively supportive of the decision," said Foster.

"If you look at the last two or three years, where players have had to make some pretty tough choices with families, it's great to be able to support him and (his wife) and their family."

New Zealand lead the Rugby Championship standings with 10 points from the first four games, with South Africa, Australia and Argentina all a point behind with two matches remaining in a competition no team has managed to dominate.

Foster attributed the tournament's competitiveness to improvements made by the Michael Cheika-coached Argentines, who have notched up wins over the All Blacks and Wallabies in this year's event.

"It's a very even competition, so that's probably where our eyes are firmly at the moment," said Foster.

"It is definitely unusual, but it's a sign that Argentina are certainly growing as a team, all their squad is now based in the Northern Hemisphere so they've been playing a lot of high competition games in the last couple of years.

"They've certainly reaped the rewards of that."

The All Blacks have struggled for form so far this year, losing a home series against Ireland before slipping to Rugby Championship defeats against South Africa and Argentina.

Foster, though, is confident his team are ready for the meeting with the Wallabies.

"The mindset's good," he said. "We've had a few days off. We'd like to get over there and really start our work.

"It's a big series, we all know the state of the Rugby Championship, it's a very even competition and every game matters."