The 29-year-old Wawrinka has had his preparation for the Championships interrupted by the illness, which led him to withdraw from an exhbition and unable to practice for two days. However, he is reported to be improving.
"He is on medication, but not antibiotics," spokesperson Fabienne Benoit told Sportinformation. "He had a fever of Tuesday, but is already a bit better."
Benoit denied a newspaper report that Wawrinka had been taken to hospital. "Doctors came to see him at the house he rents at Wimbledon for some tests," she said.
Wawrinka also wrote on Twitter that he will try to be ready for Wimbledon. The world No. 3 reached the semifinals of Queen's a week ago, and is seeded fifth for Wimbledon.
Ferrer, who withdrew from 's-Hertogenbosch this week with a stomach problem, also wrote on Twitter that he will be playing the grass-court major. "After tests, told that I can play next week," he wrote in Spanish. "Tonight we fly to London."
Ferrer, 32, is the seventh seed for Wimbledon.