Djokovic knows 'history is on the line' at Tokyo Olympics
Novak Djokovic, of Serbia, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, of Serbia, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Jul. 22, 2021 05:41 AM EDT
Novak Djokovic, of Serbia, right, and Alexander Zverev, of Germany, walk off the court 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, right, and Alexander Zverev, of Germany, walk off the court after their practice for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo. (AP Photo/Charlie Riedel)

Jul. 22, 2021 02:16 AM EDT
Novak Djokovic, of Serbia, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, of Serbia, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Jul. 22, 2021 05:46 AM EDT
Novak Djokovic, of Serbia, practices 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, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo. (AP Photo/Charlie Riedel)

Jul. 22, 2021 02:13 AM EDT
Novak Djokovic, of Serbia, cools off during 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, cools off during practice for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo. (AP Photo/Charlie Riedel)

Jul. 22, 2021 02:17 AM EDT
Novak Djokovic, of Serbia, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Novak Djokovic, of Serbia, practices for the men's tennis competition at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Patrick Semansky)

Jul. 22, 2021 05:40 AM EDT