HONG KONG -- Japanese tennis star Naomi Osaka is targeting on winning a gold medal at the 2020 Tokyo Olympic Games after she has been forced to withdraw from the 2018 Hong Kong Tennis Open due to a back injury here on Monday.

"I really want to experience the moment and at the same time, I know I want to win the gold medal. Everyone who plays in the Olympics wants to win gold, so that would be my aim," Osaka said.

Osaka became the second Japanese woman tennis player to reach No 4 in the world rankings.

Osaka said: "Sadly, I have to withdraw from this tournament, that is one of my favorite tournaments. It (her injury) is not 100 percent recovered right now."

Osaka started this year as No 68 but soared up the rankings with titles at Indian Wells in March and the US Open last month.

"I keep moving, I don't really stay in one spot. I haven't had that mental space to think I just won the US Open. For me, the year has not done yet, so I want to keep playing and see how far I can get," added Osaka.

Osaka finished runner-up at the Toray Pan Pacific Open in Tokyo last month and reached the semifinals of the China Open which concluded last Sunday, and she also has qualified for the season-ending WTA Finals Singapore for the first time in her career.