Naomi Osaka, Barbora Krejcikova out of Dubai championships

Four-time Grand Slam champion Naomi Osaka and Barbora Krejcikova have pulled out of the Dubai Tennis Championships.

Osaka is still trying to find her feet on tour after returning to the circuit last month following a maternity break.

The Japanese player fell in the first round of the Australian Open and in Abu Dhabi, and lost to Karolina Pliskova in the Qatar Open quarterfinals on Thursday.

"I'm really sorry that I have to withdraw from the Dubai Tennis Championships this season," Osaka, whose last appearance in the event was five years ago, said in a statement on the tournament's website.

Former French Open champion Krejcikova, who won her maiden Dubai title last year after defeating world No. 1 Iga Swiatek in straight sets, withdrew because of a back injury.

"This decision wasn't easy, especially given my fond memories and anticipation to compete again. However, my back injury requires further healing time. But I am committed to returning stronger next year," the 28-year-old Czech player said.