Maria Sharapova and Madison Keys have withdrawn from next week's Nature Valley Classic in Birmingham as they look to regain full fitness ahead of Wimbledon.
Sharapova, the 2004 Wimbledon champion, has decided to take a break after reaching the French Open quarter-finals.
The 31-year-old said in a statement: "I need to take care of my body and make sure I stay healthy.
"Sometimes that means you have to take tough decisions like this one."
Keys, 23, will miss the Birmingham event due to an abdominal injury.
She reached the semi-finals in Paris before losing to her fellow American Sloane Stephens.