Last year's Australian Open winner Caroline Wozniacki has been forced to pull out of the Dubai Duty Free Tennis Championships due to a viral illness.
The number nine seed's place in the tournament was handed to Polona Hercog, who lost in three sets to Lucie Hradecka in qualifying.
Wozniacki won the Dubai title in 2011 and lost to Elina Svitolina in the final two years ago.
The Danish player was also forced to withdraw from last week's Qatar Open with the same viral issue.
Meanwhile, Russia's Daria Kasatkina produced an excellent comeback to beat the Polish qualifier Magdalena Frech 6-3 3-6 6-4 in the opening round in Dubai.
The 11th seed was losing 3-0 in the deciding set but reeled off five games in a row to confirm her place in the second round.
Former world number one Garbine Muguruza had to recover from a sluggish start to see off the Ukrainian teenager Dayana Yastremska 4-6 6-3 6-3.
Muguruza, who won eight of her 11 break-point opportunities, will face China's Zheng Saisai in the second round.
The Spaniard is 1/7 to win the match while Simona Halep is 1/6 to get the better of Eugenie Bouchard. Muguruza can also be backed at 9/1 to win the French Open in June and at 12/1 to triumph at Wimbledon.
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