Serena Williams retired out of her third-round game at Indian Wells while trailing Garbine Muguruza 6-3 1-0.
She won the first 3 games of the game but called for the trainer after losing six straight to the Spaniard.
The American took to the court for its second group, but retired after world number 20 Muguruza held at the opening game.
Williams was seeded 10th in her first championship since a quarterfinal exit at the Australian Open.
“We have played many times and it’s always super-tough, super-exciting,” said Muguruza, like Williams a former world number one.
“I wish I will find her soon and [she’s] feeling “