(CNN) -- The Williams sisters have not had it easy in recent years. Two of the modern era's most successful women tennis players have been beset by health problems which have deprived the game of two of its most marketable stars. 

Serena has overcome life-threatening blood clots on both lungs, while older sibling Venus is this week making her long-awaited WTA Tour comeback as she battles a debilitating illness that has sidelined her since last year's U.S. Open. 

After pulling out of her second-round match in New York, Venus revealed she had been diagnosed with Sjogren's syndrome -- an incurable condition which affects energy levels and causes pain in the joints. 

"I just didn't feel well before my second-round match, to the point where I couldn't play," the 31-year-old told CNN's Connect the World show. 

"At the beginning of the tournament, I wasn't sure how far I would get or what I would do, I was kind of living on a hope and a dream." 

After a glittering 18-year professional career which has seen her become the first black woman to be ranked world No. 1 in the Open era, winning seven grand slam singles titles and 12 major doubles crowns alongside Serena, Williams would have been forgiven for deciding to chuck in the towel. 

But, instead of eying an early retirement, the winner of three Olympic gold medals set her sights on managing her illness and returning to the baseline ahead of this year's London Games. 

"When you don't feel well and things are taken away from you, it's hard to stay positive," the former world No. 1 said. "But, for me, it is not an option to get negative or to feel sorry for myself. 
where did she play her second round match?
New York,