Wimbledon champion Elena Rybakina pulled out of the French Open shortly before her third-round match because of illness.
One of the favourites for the title at Roland Garros, the 23-year-old Kazakh was set to play Spain's Sara Sorribes Tormo at 10:45 BST on Saturday.
"I was not sleeping well two days. I had fever, headache," she said.
"It's difficult to perform, to run and even breathe. So I think that was the only right decision I could make."
Rybakina, seeded fourth, was seen as a main contender for the clay-court Grand Slam, having won the recent Italian Open and breezed through her opening two matches without dropping a set.