Bertens threw in the towel while trailing 3-1 in the opening set on Court Philippe Chatrier.
"This morning I woke up at 3:00, and then I felt really sick. Vomiting, diarrhoea all night long, all day long," Bertens told reporters.
"I felt a little bit better before the match. I had some sleep, and I just wanted to give it a try, but then as soon as I start warming up right before the match, it started again.
"There was not any energy left."
The 27-year-old earned her favourite tag with a fine run-up to the tournament, winning the title at the Madrid Open before reaching the semi-finals at the Italian Open.
(Reporting by Julien Pretot; Editing by Ed Osmond and Alison Williams)
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