Serena Williams retired from her third-round match at Indian Wells while trailing Garbine Muguruza 6-3 1-0.
The 37-year-old won the first three games of the match but called for the trainer after losing six in succession to the Spaniard.
She took to the court for the second set, but retired after world number 20 Muguruza held in the opening game.
Williams was seeded 10th in her first tournament since a quarter-final exit at the Australian Open.
“Before the match I did not feel great and then it just got worse with every second – extreme dizziness and extreme fatigue,” the American said in a statement.
“By the score it might have looked like I started well, but I was not feeling at all well physically. I will focus on getting better and start preparing for Miami.”
Muguruza, who beat Williams in the 2016 French Open final, next faces seventh seed Kiki Bertens, who beat Britain’s Johanna Konta.
“We’ve played many times and it’s always super-tough, super-exciting,” said Muguruza, like Williams a former world number one.
“I wish I’m going to see her soon and [she’s] feeling better.”
World number two Simona Halep survived a strong challenge from Ukrainian qualifier Kateryna Kozlova to reach the fourth round.
The Romanian, who won the title in 2015, struggled to hit her stride but emerged with a 7-6 (7-3) 7-5 victory in her first meeting with the 114th-ranked Kozlova.
In the men’s competition, Roger Federer began his bid for a record sixth Indian Wells title with a 6-1 7-5 victory over German world number 85 Peter Gojowczyk to reach the third round.
However, the Swiss world number four broke straight back then benefited from a Gojowczyk double-fault for another break before serving out for victory.
Japan’s Kei Nishikori narrowly avoided a second-round defeat against Adrian Mannarino before battling through 6-4 4-6 7-6 (7-4).
Mannarino served for the match at 6-5 but double-faulted on the third break-point he faced in the game and, in the deciding tie-break, Nishikori raced into a 6-2 lead.
The Frenchman saved two match points before the Japanese finally wrapped up victory after two hours and 33 minutes.