New Zealand Rugby Union (NZRU) chief executive Steve Tew has expressed his concern over Japan's readiness for their introduction into Super Rugby.
Japan will have a representative in Super Rugby in 2016, with expansion team the Sunwolves among three new entrants as the competition expands to 18 teams.
A team from Argentina and a sixth entry from South Africa have been added to Super Rugby.
But the biggest worry comes from Japan ahead of the start of the season in February.
"We're all very excited by what the Japanese achieved at Rugby World Cup but we remain pretty nervous about their readiness for Super Rugby, and that's their next step forward," said Tew.
"I wouldn't say it's shaky, but we are concerned about any expansion when you bring new teams into a competition, and it takes a bit of time for them to bed down.
"They have not announced a coach yet so that is clearly an issue and they have not got a playing roster completely full so they are the two issues they have to put their foot on the throttle for.
"On the upside it looks like the Argentinian side will be in very, very good shape. They've got a very strong playing roster and they might actually be a considerable worry."
The Sunwolves open their inaugural Super Rugby campaign at home to the Lions in Tokyo on February 27.