PARIS (AFP) - Tournament favourite Serena Williams has pulled out of tennis' Dubai Open through illness, the organisers announced on Saturday.

In a short Twitter statement, the tournament organisers said Williams as well as Canada's Eugenie Bouchard, a wildcard entry, had both withdrawn from the tournament, which starts on Sunday.

Williams, winner of 19 Grand Slam singles titles following her success at last month's Australian Open, has been suffering from a nagging cough since that triumph.

She was forced to sit out the second day of the United States' 4-1 Fed Cup win over Argentina in Buenos Aires last weekend and was replaced by Coco Vandeweghe.

Bouchard was forced out of the event by an arm injury.

Williams has failed to win the Dubai title in four attempts, while her older sister Venus is defending champion.

Serena is next scheduled to pay in the Indian Wells tournament next month, where she has not appeared since she and Venus decided to boycott the event 14 years ago after the now-notorious hostility of spectators.

Venus, though, apparently does not plan to join Serena on an emotional return to southern California.