CHARLESTON, South Carolina (AFP) - Six-time Grand Slam winner Venus Williams pulled out of the WTA's Family Circle Cup on Wednesday, saying she will miss the next four weeks with an illness.

"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 in the quarter-finals 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.

"I am not going to get any further into it but of course I love the sport," the American Williams was quoted as saying in Wednesday's Los Angeles Times.

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

Charleston tournament director Robin Reynolds was disappointed with the illness news.

"It's unfortunate that Venus was forced to withdraw due to illness, and we wish her a quick return to the tour," Reynolds said.

The Family Circle Cup is scheduled to begin on Saturday. Australian Open champion Maria Sharapova and Venus' sister, Serena Williams, highlight the field.