Novak Djokovic, of Serbia, gestures after defeating Jan-Lennard Struff, of Germany, in the second round of the tennis competition at the 2020 Summer Olympics, Monday, July 26, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, of Serbia, right, talks with Alexander Zverev, of Germany after their practice for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo. (AP Photo/Charlie Riedel)

Novak Djokovic, of Serbia, returns to Alejandro Davidovich Fokina, of Spain, during the third round of the men's tennis competition at the 2020 Summer Olympics, Wednesday, July 28, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Hugo Dellien, left, of Bolivia, speaks with Novak Djokovic, of Serbia, after losing to Djokovic during the tennis competition at the 2020 Summer Olympics, Saturday, July 24, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Nina Sojanovic, left, and Novak Djokovic, of Serbia, high five during a first round mixed doubles tennis match against Luisa Stefani and Marcelo Melo, of Brazil, at the 2020 Summer Olympics, Wednesday, July 28, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)