A ball is seen on the court during a training session of Serbia's Novak Djokovic for the 2013 French Open tennis tournament, at Roland Garros stadium in Paris, Saturday May, 25, 2013. (AP Photo/Christophe Ena)
A ball is seen on the court during a training session of Serbia's Novak Djokovic for the 2013 French Open tennis tournament, at Roland Garros stadium in Paris, Saturday May, 25, 2013. (AP Photo/Christophe Ena)
