Serena Williams, the world number one, and Victoria Azarenka, the only unbeaten leading player on the women's tour this year, have been penalized for their late withdrawals from the Dubai Open.

Williams, who had a bad back and withdrew on Wednesday, has had $50,000 forfeited from the WTA's bonus pool, and zero points imposed for one tournament on her world ranking calculation.

Azarenka, who had a bruised heel and withdrew on Monday, had $100,000 forfeited from the WTA's bonus pool and zero points imposed for one tournament on her rankings calculation.