Two-time defending champion Petra Kvitova has withdrawn from next week's Nature Valley Classic in Birmingham, while Karolina Pliskova has accepted a wildcard into the LTA grass-court event.
Kvitova is still recovering from a left forearm injury that forced her to pull out ahead of the French Open.
She lifted the trophy in 2017 in just her second tournament back following the horrific knife attack that nearly ended her career and defeated Magdalena Rybarikova 12 months ago to retain the title.
"I'm sorry that I don't have great news for you," said Kvitova in a video update on social media.
"I won't be able to compete in Birmingham this year. But, I have the best memories from Birmingham, it was the first place that I won a title when I came back after the injury and I'm always enjoying my time there.
"I hope that I will see you there next year on the beautiful grass courts. Enjoy your time there, enjoy the tournament, the players and the sun - hopefully it will be a great week for you."
American Madison Keys has also withdrawn but the world No 3 Karolina Pliskova has accepted a wildcard.
"I'm very happy to be coming back to Birmingham because it has a fantastic line-up of players this year and the competition will be really strong," said Pliskova about her entry into the draw.
"There is no better way to open my grass-court season. I have great memories of playing in the final there in 2015 and I'd love to go one better this time."
Pliskova's presence means that, for the first time, the tournament will feature the top three women in the world rankings.
World number one Naomi Osaka and the newly crowned French Open champion Ashleigh Barty are already on the bill as all look to arrive at Wimbledon Championships in form.
The five-time Wimbledon champion Venus Williams, British No 1 Johanna Konta and last year's Wimbledon semi-finalist Julia Goerges, are all also in-line to compete for the Maud Watson Trophy.
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