Tennis - Adria Tour - Belgrade, Serbia - June 14, 2020 Serbia's Novak Djokovic and Germany's Alexander Zverev are seen after the final match between Austria's Dominic Thiem and Serbia's.

Serbia's Novak Djokovic and Viktor Troicki during Adria Tour at Novak Tennis Centre in Belgrade, Serbia, June 13, 2020.

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).

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Pianist Lola Astanova performs as Serbia's Novak Djokovic looks on, following the outbreak of the coronavirus disease (COVID-19).

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).

Tennis - Adria Tour - Belgrade, Serbia - June 13, 2020 Serbia's Novak Djokovic with Serbia's Viktor Troicki after winning their match.

Serbia's Novak Djokovic with his wife Jelena, his father Srdjan, his mother Dijana and his brother Marko in the stands during Adria Tour at Novak Tennis Centre in Belgrade, Serbia, June 14, 2020.

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).

Tennis - Adria Tour - Belgrade, Serbia - June 14, 2020 Austria's Dominic Thiem poses with the trophy along with Serbia's Novak Djokovic and Germany's Alexander Zverev.

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 pose for a selfie before a press conference REUTERS/Marko Djurica.

Bulgaria's Grigor Dimitrov, Serbia's Novak Djokovic, Dusan Lajovic, Austria's Dominic Thiem, Germany's Alexander Zverev pose for a photo with the ballkids during Adria Tour at Novak Tennis Centre in Belgrade, Serbia, June 12, 2020.

Tennis - Adria Tour - Novak Tennis Centre, Belgrade, Serbia - June 12, 2020 Members of the media are seen before a press conference.

Tennis - Adria Tour - Belgrade, Serbia - June 14, 2020 Austria's Dominic Thiem after winning his final match against Serbia's Filip Krajinovic.

Serbia's Novak Djokovic during Adria Tour at Novak Tennis Centre in Belgrade, Serbia, June 14, 2020.

Tennis - Adria Tour - Belgrade, Serbia - June 14, 2020 Austria's Dominic Thiem and Serbia's Filip Krajinovic pose for a picture before their final match.

Tennis - Adria Tour - Belgrade, Serbia - June 13, 2020 Serbia's Novak Djokovic in action during his match against Serbia's Viktor Troicki.

Bulgaria's Grigor Dimitov and Germany's Alexander Zverev are seen during the trophy ceremony during Adria Tour at Novak Tennis Centre in Belgrade, Serbia, June 14, 2020. Picture taken June 14, 2020.