If Japan are to remain ranked in the top eight nations in the world, they must evolve the current domestic league structure, according to Brave Blossoms head coach Jamie Joseph.
Joseph, who led Japan to their first ever Rugby World Cup quarter-final on home soil last year and eighth place in the world rankings, wants the domestic Top League competition to run from December to May so as not to interfere with the national team's test matches.
"It is detrimental to the national game if we are asking our players to play test matches then Top League and then test matches, and be successful at both," said Joseph, according to Kyodo News.
"First and foremost, for us to keep improving as a team we must prioritise the welfare of our players."
"The World Cup results were evidence that when we get that right the players can achieve anything. And I believe we need a Top League structure that allows our players to achieve this."
Joseph, who signed on to coach Japan for another four years following the World Cup, has been frustrated in the past at not having players available for the Brave Blossoms due to their Top League commitments.
Japan's Top League competition, which this year features the likes of Dan Carter, Kieran Read and Will Genia, usually runs from September through January.
However, because of last year's World Cup, the start of the competition was postponed until earlier this month.
On Tuesday, the Japan Rugby Football Union did announce that a new league would replace the Top League from 2021.
However, no details were given around the timing of the new competition.
"We need to ensure that we have a competition structure that avoids (schedule conflict) at all costs," said Joseph.
"If we have the right structure then the Japan team will get better. If not it will be very difficult to win."
Joseph will lead the Brave Blossoms in home fixtures against Wales and England in June and July this year.
Japan are also due to face Argentina, Scotland, Ireland and the Barbarians in October - December, a period of time that would usually clash with Top League fixtures.
(Reporting by Jack Tarrant; Editing by Michael Perry)
