Gilles Muller, of Luxembourg, returns a shot to Kei Nishikori, of Japan, at the BNP Paribas Open tennis tournament, Tuesday, March 14, 2017, in Indian Wells, Calif. (AP Photo/Mark J. Terrill)
Serbia's Novak Djokovic serves in the second round match of the French Open tennis tournament against Luxembourg's Gilles Muller at the Roland Garros stadium, in Paris, France, Thursday, May 28, 2015. (AP Photo/Francois Mori)