World number one Simona Halep withdrew from the WTA Connecticut Open with a leg injury, the day after losing the Cincinnati final to Kiki Bertens.
The Romanian, who cited soreness in her right Achilles, said she still plans to take part in the upcoming US Open.
"I need to recover in time for the US Open," she said.
This would have been Halep's third tournament in as many weeks. She won the WTA Montreal event before being runner-up in Cincinnati, losing in three sets to Dutchwoman Bertens on Sunday.
"I really wanted to play it (Connecticut) and I saw that many fans bought tickets to see me here, but I feel very sore with my Achilles, and I need some rest," she added.
"I had so many matches in the last two weeks, so it's tough. See you next year, and all the best."
The 26-year-old Halep will be replaced in the draw by lucky loser Belinda Bencic of Switzerland.
American CoCo Vandeweghe also pulled out of the hardcourt tournament in New Haven on Sunday with a sore right ankle.
In Monday action, two-time Wimbledon winner Petra Kvitova overpowered 2016 champion Agnieszka Radwanska 6-1, 7-6 (7/3) and fourth-seeded Karolina Pliskova of the Czech Republic was knocked out by Russian Ekaterina Makarova 6-1, 6-3.
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