Naomi Osaka dropped from 14th to 85th in the singles world rankings announced Monday by the Women's Tennis Association, falling out of the top 50 for the first time since February 2018.

With the rankings reflecting players' records over the past year, Osaka's lack of tournament appearances in 2021 weighed heavily following her two self-imposed breaks from tennis to care for her mental health.

The 24-year-old was looking to defend her Australian Open title this month, but suffered a third-round upset by then 60th-ranked American Amanda Anisimova.

Osaka, a four-time Grand Slam winner, pulled out of the French Open last May ahead of her second-round match, when she decided not to attend a press conference and revealed her struggle with depression.

She sat out Wimbledon before participating in the Tokyo Games — where she lit the Olympic cauldron during the opening ceremony — but lost in the third round in late July and exited the U.S Open at the same stage in September before taking another break.

She returned earlier this month and reached the semifinals in the Melbourne Summer Set 1, the Australian Open warm-up event.

Misaki Doi is currently ranked the highest among Japanese at 72nd.

Australian Open winner Ash Barty of Australia topped the ranking, followed by Aryna Sabalenka of Belarus in second and Barbora Krejcikova of the Czech Republic in third.