Alexander Zverev of Germany returns with a backhand to Daniil Medvedev of Russia during their singles final tennis match of the ATP World Tour Finals, at the Pala Alpitour in Turin, Italy, Sunday, Nov. 21, 2021. (AP Photo/Luca Bruno)

Daniil Medvedev of Russia gestures during his singles final tennis match of the ATP World Tour Finals against Alexander Zverev of Germany, at the Pala Alpitour in Turin, Italy, Sunday, Nov. 21, 2021. (AP Photo/Luca Bruno)