Japanese tennis superstar Naomi Osaka announced on Friday she was splitting with her coach, her second break-up this year as she battles for form and slips down the world rankings. On the eve of the Pan Pacific Open tournament in Osaka, western Japan, the 21-year-old announced she would no longer be working with Jermaine Jenkins, who joined her team after her triumph at the Australian Open in January.

"Writing this to let you guys know that me and Jay won't be working together anymore," Osaka tweeted. "I'm super grateful for the time we spent together and the things I learned on and off the court but I feel like now is a (sic) appropriate time for a change... Thank you for everything, it was a blast," added Osaka.