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 has released a statement saying she was confined to bed, but hoped to be fit for Wimbledon.
Kvitova, who won her second Wimbledon title by beating Eugenie Bouchard in last year's final, is the world number two but hasn't played since losing in the fourth round of the French Open at the start of this month.
Meanwhile the New Zealander Marina Erakovic has been beaten in the first round of singles at the Eastbourne grass court tournament.
Erakovic, who came through qualifying, was beaten in straight sets by Tsvetana Pironkova of Bulgaria.
She is also playing doubles this week with Eugenie Bouchard of Canada.
Wimbledon starts next week.