A Japanese comedy duo have apologised to tennis star Naomi Osaka after they reportedly said she "needed some bleach" and "is too sunburned" during a live match.

The 21-year-old Australian Open champion won her first trophy since her win in Melbourne, emerging victorious for the first time at the Pan Pacific Open in her hometown, Osaka on Sunday.

'A Masso', a comedy duo comprising two females, Ai Murakami and Aiko Kanour, have apologised but without mentioning Osaka's name. Murakami wrote "We sincerely apologise for making the specific person feel uncomfortable, as well as for everyone else connected to the event. We also sincerely apologise for causing trouble."

Watanabe Entertainment, who manage the duo, said the pair have been severely warned and issued their own apology. They commented that the remarks were "inconsiderate of diversity in an era where diversity is respected".

This is not the first racial case Osaka has been involved in this year after Japanese noodle company Nissin was accused of "whitewashing" a cartoon depiction of the mixed-race world No 4 in January. The company said the "whitewash" had not been intentional and they would pay more close attention to diversity issues.

Osaka has not commented.