Venus Williams pulled out of the WTA's Family Circle Cup on Wednesday citing an undisclosed illness that will keep her sidelined for the next four weeks.      

"I regret that I will not be participating in the Family Circle Cup," said Williams, who declined to go into detail. "I wish the tournament my best and look forward to returning to competitive play in Rome the week of May 12."      

Williams, the world number six, said last week she was dealing with an undisclosed medical problem. She lost last week to Russian Svetlana Kuznetsova in the quarter-finals of the Sony Ericsson Open.      

"I've just been having some issues that I need to resolve, so I am working on that at the moment and I am hoping to be back playing soon as possible," she told the Los Angeles Times. "I am not going to get any further into it but of course I love the sport."       

Williams will not compete for the USA in the Fed Cup semi-final against Russia on April 26-27.

Meanwhile, her sister Serena will participate as scheduled in the Family Circle Cup, which is scheduled to begin on Saturday.