BELGRADE, SERBIA - JUNE 14: Alexander Zverev of Germany returns during his match against Novak Djokovic of Serbia on June 14, during the 3rd day of Summer Adria Tour, 2020 in Belgrade, Serbia. (Photo by Nikola Krstic/MB Media/Getty Images)
BELGRADE, SERBIA - JUNE 14: Alexander Zverev of Germany returns during his match against Novak Djokovic of Serbia on June 14, during the 3rd day of Summer Adria Tour, 2020 in Belgrade, Serbia. (Photo by Nikola Krstic/MB Media/Getty Images)