British number one Katie Boulter retired from her first round match against Ukraine's Anhelina Kalinina with illness at the Birmingham Classic.

The 27-year-old was playing two days after retaining her Nottingham Open title, having coming back from a set down to beat Karolina Pliskova just hours after completing a three-set win over Emma Raducanu.

Boulter received a medical timeout in the first set and decided she could not continue after losing the opener 6-3 to Kalinina.

She later confirmed she was "fine" and said she had been motivated to still compete in Birmingham in an attempt to secure a seeding at Wimbledon.

"Obviously a long 10 days. I wanted to come up here anyway, I wanted to try, but I'm just not quite ready yet," said Boulter, who plans to play at Eastbourne next week.

"I was quite sick during Nottingham but I just tried to stay in the tournament as long as I possibly could, as bad as I was feeling.

"From my third match I was really struggling. But I just tried to get through it and finish the week. It's probably a little bit of a combination of everything."

Boulter is 31st in the world rankings, with only the top 32 guaranteed to be seeded at Grand Slams, but she added it was "not the be all and end all" should she slip from those positions.

Earlier, Caroline Wozniacki's first match on a grass court in five years ended in defeat by Elise Mertens.

Former world number one Wozniacki, who won the Australian Open in 2018, lost 6-4 6-1 to Belgian fifth seed Mertens.

Denmark's Wozniacki, 33, returned to tennis last year, three and a half years after she retired at the 2020 Australian Open.

Britain's Harriet Dart advanced to the second round with a 6-3 6-3 win over Japanese qualifier Moyuka Uchijima.

But Heather Watson suffered a 3-6 6-4 7-5 loss to eighth seed Marie Bouzkova in a tussle lasting two hours and 53 minutes.

Watson took a medical timeout after the second set and led 5-2 in the decider before Bouzkova hit back.

"I am super tired but I think it was a great match. What a way to start the grass-court season," said Bouzkova.

Briton Amelia Rajecki was beaten 7-5 6-3 by Russian Diana Shnaider in her first WTA main draw match.