Serena Williams, who won her 19th Grand Slam title at the Australian Open last month while struggling with a persistent virus, has withdrawn from the Dubai Open, apparently suffering from the same ailment.

In a Twitter statement, officials said Williams as well as Canada's Eugenie Bouchard, a wildcard entry, had both withdrawn from the tournament, starting on Sunday.

Williams' achievement in those difficult circumstances in Melbourne was particularly remarkable, but the cost may be high and has been causing concern about the 33-year-old's long-term health.

She has been suffering from a nagging cough since that triumph and was forced to sit out the second day of the United States' 4-1 FedCup win over Argentina in Buenos Aires last weekend.

The world number one made it clear at the start of the year that she must restrict her schedule if she is to have a chance of winning the three more Grand Slam titles needed to reach Steffi Graf's open era record of 22 - and her Dubai pull-out underlines her determination to do this.

It may, though, give her a better chance of doing well at her next tournament, Indian Wells, early in March, something of unusual significance for her and for her sister Venus Williams.

It will be the first time either Williams sister has returned to Indian Wells since they boycotted the tournament after their hostile treatment by the crowd 14 years ago.

Canada's Eugenie Bouchard has withdrawn with arn arm injury. The world no 7 was beaten 4-6 6-1 6-2 by Germany’s Mona Barthel in the second round of this week's WTA Diamond Games tournament in Antwerp.