US Open champions Serena Williams and her sister Venus have both withdrawn from next week's China Open in Beijing.
In a huge blow to the tournament's organisers, Serena has pulled out of the event because of illness, while Venus is suffering from a back problem.
Serena tweeted: "Have flu, no fun."
However the world No 4 is expected to have recovered in time for the end-of-season WTA Championships in Turkey at the end of October.
Tournament director Charles Hsiung said: "We would have loved for Venus and Serena to play the China Open this year but unfortunately players get injured and sick and are unable to compete."
Meanwhile Venus, who is ranked No 41 in the world at the moment, said: "I was looking forward to playing at the China Open this year but am currently working through a minor back injury and will unfortunately need more time to recover."
The China Open gets underway on Saturday with Poland's Agnieszka Radwanska defending her title against the likes of No 1 Victoria Azarenka, Russian Maria Sharapova and home favourite Li Na.
