Japan are bidding to field a team made up solely of Japanese nationals in time for the 2007 World Cup.
Kiwi-born Andy Miller celebrates qualification with Daisuke Ohata
The Cherry Blossoms still rely heavily on naturalised players who qualify having played company rugby in the country for the last three years.
The New Zealand-born Reuben Parkinson, George Koria, Adam Parker and Andy Miller are all integral members of the squad.
But they and their other naturalised team-mates look set to face the axe in four years time.
However, Parkinson believes Japanese rugby authorities will make a major mistake if they overlook foreigners who have qualified via the country's company rugby set-up.
He told the BBC Sport website: "We've heard they are going to have no foreigners by the next World Cup. But, while it's a bold move, I don't think it's going to work out for them."
At the 1999 tournament, the starting XV included eight foreigners.
Four years on the set-up has been very different.
"This year there's been a maximum of just two of us at any one time," Parkinson added.
"They seem to think they can do fine without us, but realistically they can't. They'll definitely come unstuck.
"There are major areas where they are seriously lacking, particularly in terms of size and they look set to struggle without the bulky New Zealand-born guys in the scrum."
Japan have brought in former Wallabies Mark Ella and Mark Brown to work with their backs and forwards respectively.
The two ex-players have been heavily embroiled in recent training sessions, but Parkinson does not believe it goes far enough.
He added: "The other problem is their tradition. They have foreign coaches in to help but they feel their pride's at stake and just do their own thing.
"They can be pig-headed about karate but not about rugby. It's doing them no justice."