Petra Kvitova will start the defence of her Wimbledon title next week with no competitive grasscourt practice after pulling out of the Aegon International at Eastbourne where she was top seed.
The 25-year-old Czech said in a statement on Monday that she was confined to bed but hoped to be fit for Wimbledon.
"I have a sore throat. I have to stay in bed, drink tea and rest," said Kvitova. "I didn't feel well when I came here last Thursday.
"I hope to be fine for Wimbledon. I'll stay here in Eastbourne and then slowly move to London."
Kvitova, who won her second Wimbledon title by beating Eugenie Bouchard in last year's final, is the world number two but has not played since losing in the fourth round of the French Open at the start of June.
She had also been expected to play in the doubles at Eastbourne with Dane Caroline Wozniacki.