New Zealand are in a real fight to retain two of their biggest stars with Julian Savea and Brodie Retallick prime targets for cashed-up overseas clubs.

Both men are tipped to re-sign with New Zealand Rugby (NZR) in the coming weeks but the departures of Colin Slade and Charles Piutau in recent weeks mean the governing body won't rest easy until the duo have signed on the dotted line.

"I think if Brodie and Julian decided post Rugby World Cup to move on then it would be really bad news for us," NZR's general manager of rugby Neil Sorensen told the New Zealand Herald.

"You would have to start saying we are not doing something right here and you would have to say it was a trend. It would have been great to keep Charles [Piutau] and Colin [Slade] - but you wouldn't want to lose two more current All Blacks. We can confidently say they are world-class players but they have also got a lot of rugby ahead of them, too. I get that a player might play here in New Zealand until they are 28, 29 and then have the rest of his career offshore. I can respect that and empathise with that.

"What we don't want to do is have a whole bunch of our top 40 players disappear when they are 22, 23-year-olds. If Julian and Brodie decide they are gone as well it will be a major issue for us."

Retallick, the reigning World Rugby Player of the Year, could command a similar deal to the rumoured $NZ 700,000 figure French club Pau paid for Slade while Savea could perhaps secure a deal in excess of that with his obvious marketing potential.

But money isn't everything and NZR as two key strengths in their corner in Olympic Sevens and the British & Irish Lions series in 2017. Savea has already flagged an interest in the Sevens while Retallick, if fit, would be a walk-up start to face rugby's most famous touring side. Still, Sorensen said players needed to work out what was important to them individually.

"We have a lot of dialogue with them and their agents," Sorensen said. "Brodie is in massive demand offshore and he's also a young man, newly married, who is looking at his options which is a good thing I think.

"We don't want them to stay in New Zealand because they have to, we want them to stay in New Zealand because they want to."