"Both players remain in New Zealand with Mafi currently in police custody following an altercation between the two players.
"Rugby Australia understands that no other players were involved in the incident.
A New Zealand Police spokesperson confirmed that a 28-year-old man has been charged with injuring with intent to injure following the alleged assault.
The police confirmed the men involved in the altercation were known to each other.
"The alleged victim, also a 28-year-old man, received moderate injuries following the incident. He did not require hospitalisation," the spokesperson noted.
Melbourne Rebels chief executive Baden Stephenson was disappointed with the news.
"I am bitterly disappointed that an incident has occurred at the end of a season where we have taken pride in our on and off field behaviour," Stephenson said.
Mafi has played 21 tests for Japan and was named Australia's Super Rugby player of the season last year.
It is understood Mafi will appear in the Dunedin District Court tomorrow.