"We regret to announce that Serena Williams and Angelique Kerber have withdrawn due to illness and injury," the Dubai Duty Free Tennis Championships wrote on their official Twitter account ahead of the draw.

The news is a double blow for organisers with Williams and Kerber, the world's top two players, seeded number one and two respectively. 

The 28-year-old German shocked Williams, 34, in the Australian Open final last month to win her first Grand Slam title.

Williams, who also withdrew in 2013 and 2015, said she was suffering from flu, while Kerber blamed a right upper thigh injury.

The withdrawals follow that of Poland's Agnieszka Radwanska and Alize Cornet of France.

Defending champion Simona Halep of Romania is now the top seed in the tournament which starts on Monday with world number five Garbine Muguruza of Spain moving up to second seed.