Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Viktor Troicki, Nenad Zimonjic, Dusan Lajovic, Novak Djokovic, Austria’s Dominic Thiem, Bulgaria’s Grigor Dimitrov and Germany’s Alexander Zverev pose for a photo with the ballkids, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and former player Jelena Jankovic in action during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and former player Jelena Jankovic in action during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Members of a childrens choir pose for a photograph REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and former WTA player Serbia’s Jelena Jankovic before their doubles match, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and former player Jelena Jankovic in action during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic in action with former player Jelena Jankovic during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Fans in the stands during the doubles match between Serbia’s Novak Djokovic and former player Jelena Jankovic against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Fans in the stands during the doubles match between Serbia’s Novak Djokovic and former player Jelena Jankovic against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and former player Jelena Jankovic during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and former player Jelena Jankovic in action during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Bulgaria’s Grigor Dimitrov during a press conference REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Austria’a Dominic Thiem during a press conference REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Germany’s Alexander Zverev, Serbia’s Novak Djokovic, Bulgaria’s Grigor Dimitrov and Austria’a Dominic Thiem during a press conference REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Germany’s Alexander Zverev, Serbia’s Novak Djokovic, Bulgaria’s Grigor Dimitrov and Austria’a Dominic Thiem during a press conference REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic and children pose for a photograph REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Germany’s Alexander Zverev arriving at the Centre with his partner Olya Sharypova, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Fans in the stands during the doubles match between Serbia’s Novak Djokovic and former player Jelena Jankovic against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic, former player Jelena Jankovic, Nenad Zimonjic and Olga Danilovic after the match, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic in action with former player Jelena Jankovic during their doubles match against Serbia’s Nenad Zimonjic and Olga Danilovic, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica TPX IMAGES OF THE DAY

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Serbia’s Novak Djokovic with Bulgaria’s Grigor Dimitrov during their doubles match, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Austria’s Dominic Thiem in action with Serbia’s Novak Djokovic during their doubles match against Serbia’s Viktor Troicki and Bulgaria’s Grigor Dimitrov, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Bosnia and Herzegovina’s Damir Dzumhur, Serbia’s Filip Krajinovic, Viktor Troicki, Nenad Zimonjic, Dusan Lajovic, Novak Djokovic, Austria’s Dominic Thiem, Bulgaria’s Grigor Dimitrov and Germany’s Alexander Zverev pose for a photo with the ballkids, following the outbreak of the coronavirus disease (COVID-19) REUTERS/Marko Djurica