Japanese tennis player Kei Nishikori serves the ball to Australian Nick Kyrgios returns the ball to during their Mutua Madrid Open quarter finals match played at Caja Magica tennis complex in Madrid, Spain, on 06 May 2016. EPA/JJ GUILLEN

French tennis player Jo-Wilfried Tsonga returns a ball to Canadian Milos Raonic during their Mutua Madrid Open tennis tournament round of 16 match at the Caja Magica Tennis Center in Madrid, Spain, 05 May 2016. The Mutua Madrid Open runs from 29 April until 08 May 2016. EPA/JUANJO MARTIN

Slovak tennis player Dominika Cibulkova returns the ball to US Louisa Chirico during their Mutua Madrid Open semi-final match played at Caja Magica tennis complex in Madrid, Spain, 06 May 2016. EPA/CHEMA MOYA

British tennis player Andy Murray returns to Czech Tomas Berdych during their Mutua Madrid Open quarter final match held at the Caja Magica tennis complex in Madrid, Spain, on 06 May 2016. EPA/J.J. Guillen

Australian tennis player Nick Kyrgios returns the ball to Japanese Kei Nishikori during their Mutua Madrid Open quarter final match played at Caja Magica tennis complex in Madrid, Spain, on 06 May 2016. EPA/JJ GUILLEN