Four-times Grand Slam champion Naomi Osaka and holder 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 quarter-finals 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.

Osaka falls at first hurdle in Abu Dhabi

Former French Open Krejcikova champion, who won her maiden Dubai title last year after defeating world number one Iga Swiatek in straight sets, withdrew due to 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 Czech 28-year-old said.