Coaches Tony Brown (L) and Jamie Joseph watch as the Sunwolves take on the Crusaders at AMI Stadium in Christchurch earlier this year. Photo: Getty
The Sunwolves, who have three games left in the season, will be coached by another former Highlanders coach in Tony Brown.
Brown works as Joseph's attack coach for both the Sunwolves and the Japanese national team.
In a statement the Sunwolves said Joseph would return to New Zealand in July to recover from a minor procedure on his back.
This would enable him to be fully focused on Japan's Rugby World Cup preparations.