Grigor Dimitrov of Bulgaria returns the ball to Gael Monfils of France during their quarter final match at the Monte-Carlo Rolex Masters tournament in Roquebrune Cap Martin, France, 17 April 2015. EPA/SEBASTIEN NOGIER

Gael Monfils of France celebrates during his quarter final match against Grigor Dimitrov of Bulgaria at the Monte-Carlo Rolex Masters tournament in Roquebrune Cap Martin, France, 17 April 2015. EPA/SEBASTIEN NOGIER

Rafael Nadal of Spain returns the ball to David Ferrer of Spain during their quarter final match at the Monte-Carlo Rolex Masters tournament in Roquebrune Cap Martin, France, 17 April 2015. EPA/SEBASTIEN NOGIER

Milos Raonic of Canada (L) and Tomas Berdych of Czech Republic (R) after Raonic retired from the match during his quarter final match at the Monte-Carlo Rolex Masters tennis tournament in Roquebrune Cap Martin, France, 17 April 2015. EPA/SEBASTIEN NOGIER

Novak Djokovic of Serbia returns the ball to Marin Cilic of Croatia during their quarter final match at the Monte-Carlo Rolex Masters tournament in Roquebrune Cap Martin, France, 17 April 2015. EPA/SEBASTIEN NOGIER