American sisters Serena and Venus Williams will play no part in this year's China Open, organisers have confirmed.

Serena, who won Wimbledon, an Olympic gold medal and the US Open, is believed to be suffering from flu, while Venus is thought to have picked up a back injury, which has forced the duo out of the tournament just days before the opening round.

"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," said tournament director Charles Hsiung.

"We hope that they both recover quickly and look forward to them returning to the National Tennis Stadium in 2013."

Meanwhile, Agnieszka Radwanska will attempt to defend her title in Beijing when the competition gets underway tomorrow.