MELBOURNE, AUSTRALIA - JANUARY 13: Novak Djokovic of Serbia serves during a practice session ahead of the 2017 Australian Open at Melbourne Park on January 13, 2017 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)
MELBOURNE, AUSTRALIA - JANUARY 13: Novak Djokovic of Serbia serves during a practice session ahead of the 2017 Australian Open at Melbourne Park on January 13, 2017 in Melbourne, Australia. (Photo by Michael Dodge/Getty Images)