England coach Eddie Jones has slammed the decision to cut the Sunwolves from Super Rugby.
Jones, the former Japan coach, said a Japanese team in Super Rugby was vital to the nation's test growth.
And he called on the Japan union to find an alternative.
"The purpose of the Sunwolves was to give opportunities for young Japanese players to prepare for test rugby," Jones told the Kyodo news agency.
"What Japan was missing was that opportunity for younger players to go from a good domestic Top League into a higher level of competition without being exposed to test level, and the Sunwolves provided that opportunity.
"It hasn't worked out for them and I think it is a massive opportunity missed."
SANZAAR have turfed the Sunwolves out of the competition after the 2020 season, despite the Japanese team's improved performances.
Observers say the decision could not have come at a worse time, given the proximity to this year's World Cup in Japan.
Jones' words echo those of Wild Knights coach Robbie Deans, who said Japan needed a team which bridged the gap between its domestic competition and test rugby.
Jones was in charge of Japan when it beat Wales and South Africa in landmark moments.
"If Japan wants to be a top 10 country in the world, which they do, they need their players to be prepared," Jones said.