The Serbian mixed doubles team of Nina Stojanovic, left, and Novak Djokovic play during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

The Serbian mixed doubles team of Nina Stojanovic, left, and Novak Djokovic play during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

The Serbian mixed doubles team of Nina Stojanovic, left, and Novak Djokovic play during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)

The German mixed doubles team of Laura Siegemund, left, and Kevin Krawietz play during the quarterfinals of the tennis competition at the 2020 Summer Olympics, Thursday, July 29, 2021, in Tokyo, Japan. (AP Photo/Seth Wenig)