Federer told organizers of the Kooyong Classic in Melbourne doctors advised he take time off because of the illness and "therefore, as a precaution, I will need to withdraw from Kooyong."

Federer posted a statement on his Web site saying he became ill when he arrived in Australia last Friday. After his condition worsened during the weekend, he was examined by physicians.

"The doctors have advised me that I should take a couple of days off and recuperate so that I am able to be 100 percent for the start of the Australian Open," Federer said.

Federer is a two-time defending champion at the Australian Open. That tournament, the year's first Grant Slam event, opens Jan. 14.

Federer was beaten by Andy Roddick in the final of the 2007 Kooyong Classic, which is considered an exhibition rather than a tournament.