Japan’s Naomi Osaka retired from her second-round match against Dalila Jakupovic in Birmingham with an abdominal problem.

Osaka, ranked 18th in the world, struggled on serve and lost the first set 6-3 before calling for the trainer.

She previously struggled with an abdominal injury during last year’s hard-court season.

Slovenian qualifier Jakupovic now faces Slovakia’s Magdalena Rybarikova in the Nature Valley Classic quarter-finals.

Rybarikova, who reached the Wimbledon semi-finals last year, overcame Kristina Mladenovic of France 3-6 6-2 6-1.

Second seed Elina Svitolina reached the last 16 in Birmingham for the first time with a 6-4 6-2 win over Alize Cornet of France.

The Ukrainian will play Romania’s Mihaela Buzarnescu on Friday, following her 4-6 6-3 6-2 win over Czech Petra Martic.

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Osaka is scheduled to play in the WTA event at Eastbourne, which begins on 25 June.

Despite the injury, she hit nine winners against Jakupovic, but the big-hitting Slovenian broke to love in the seventh game.

Osaka was unable to capitalise on two break points in the next game and she struggled to generate power on her serve, eventually retiring after 33 minutes.

“It’s never nice to win when somebody’s injured. I feel sorry for her,” Jakupovic told Eurosport.

“I was trying to focus on my play and I didn’t really look on her side, but I hope she’s going to be better for her next tournament.”

At the WTA event in Mallorca, former world number one Angelique Kerber fell 5-7 6-2 6-1 to American Alison Riske, and French top seed Caroline Garcia beat Sweden’s Johanna Larsson 6-4 6-3.