LONDON, ENGLAND - NOVEMBER 08: Novak Djokovic of Serbia plays a forehand in a training session during previews for the Nitto ATP World Tour Finals at The O2 Arena on November 08, 2019 in London, England. (Photo by Alex Pantling/Getty Images)
LONDON, ENGLAND - NOVEMBER 08: Novak Djokovic of Serbia plays a forehand in a training session during previews for the Nitto ATP World Tour Finals at The O2 Arena on November 08, 2019 in London, England. (Photo by Alex Pantling/Getty Images)