Germany's Alexander Zverev, left, Serbia's Novak Djokovic, second left, Bulgaria's Grigor Dimitrov, second right, and Austria's Dominic Thiem attend a press conference prior a a charity tournament Adria Tour, in Belgrade, Serbia, Friday, June 12, 2020. Serbian tennis player Novak Djokovic set up a series of tennis tournaments in the Balkan region while the sport is suspended amid the coronavirus pandemic. (AP Photo/Darko Vojinovic)