Venus Williams of the US hits a return to Serena Williams of the US during their quarterfinals match on the ninth day of the 2015 US Open Tennis Championship at the USTA National Tennis Center in Flushing Meadows, New York, USA, 08 September 2015. The US Open runs through 13 September, which is a return to a 14-day schedule. EPA/ANDREW GOMBERT

Venus Willams of the USA returns the ball to Agnieszka Radwanska of Poland during their quarter final match of the the WTA Qatar Ladies Open tennis tournament at the International Khalifa Tennis Complex in Doha, Qatar, 26 February 2014. EPA/STRINGER

Venus Williams of the USA in action against Urszula Radwanska of Poland during their 2nd round match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 26 March 2015 EPA/RHONA WISE

Venus Williams of the US in action against Johanna Konta of Britain in the first round match on day two of the Australian Open tennis tournament in Melbourne, Australia, 19 January 2016. EPA/DAVID CROSLING

Venus Williams of the USA in action against Sloane Stephens of the USA during their first round match for the French Open tennis tournament at Roland Garros in Paris, France, 25 May 2015. EPA/ETIENNE LAURENT