All Blacks coach fears losing top players

New Zealand assistant coach Ian Foster hopes that the likes of Israel Dagg and Ben Smith will be persuaded to reject moves overseas.

Dagg, Smith and Aaron Cruden, who has long been linked with Montpellier, could all leave New Zealand when their contracts expire.

While Cruden has lost the fly-half starting role in 2016 to Beauden Barrett, the new World Player of the Year, the combination of Dagg and Smith in the back three has been phenomenal for New Zealand this year.

"There's a definitely a fear we could lose them," Foster told Newstalk ZB.

"We just have to do whatever we can, and say whatever we can, and then we have to give these guys space.

"At the end of the day, these guys are grown-ups. They are making a tough decision and there is no question they love the black jersey."

Foster also warned that players in the past had moved overseas too early, missing out on Test caps as a result. Dan Carter, Ma'a Nonu and Conrad Smith all move to France after last year's Rugby World Cup win in their mid-30s.

"A lot of these guys have the ability to play for another two or three years and then still look at going overseas for a couple of years," he added.

"I think the players that seem to regret it are the guys who go over a little bit early and in two years time find they're still playing great rugby but they've given up on the All Blacks dream."