Venus and Serena Williams have been beset by health issues in recent times . The former world number one has had a series of operations on her left knee since the end of last year but is still able to play at Wimbledon this week. Seven-time grand slam winner Venus makes her return to the WTA Tour on Wednesday . The former world No . 1 has not played since pulling out of the U.S. Open in August 2011 .
Venus and Serena Williams have been beset by health issues in recent times . Serena suffered blood clots on her lungs , and Venus has Sjogren 's syndrome . Seven-time grand slam winner Venus makes her return to the WTA Tour on Wednesday . The former world No . 1 has not played since pulling out of the U.S. Open in August 2011 .