Andy Murray of Great Britain in action against Lukas Rosol of the Czech Republic during their quarterfinal match at the ATP Tennis Tournament in Munich, Germany, 02 May 2015. EPA/PHILIPPE RUIZ

US tennis player Serena Williams (R) and Danish Caroline Wozniacki (L) during a charity event held on the ocassion of the Mutua Madrid Open tennis tournament at the Caja Magica pavillion in Madrid, Spain, 01 May 2015. The Mutua Madrid Open takes place at the Caja Magica pavilion in Madrid from 01 to 10 May 2015. EPA/JUANJO MARTIN

Australian Nick Kyrgios in action against Netherland’s Tobin Haase on the fifth day of the Estoril Open tennis tournament in Estoril, Cascais , 01 May 2015. EPA/TIAGO PETINGA

An umbrella sits in the empty stands at Center Court before the start of quarterfinal matches at the ATP Tennis Tournament in Munich, Germany, 01 May 2015. EPA/ANDREAS GEBERT

Roger Federer of Switzerland serves the ball to Diego Schwartzman of Argentina during their semifinal match at the TEB BNP Paribas Istanbul Open tennis Tournament in Istanbul, Turkey 02 May 2015. EPA/TOLGA BOZOGLU