Barclays ATP World Tour Finals - Day Eight [Getty Images]

LONDON, ENGLAND - NOVEMBER 16: Roger Federer of Switzerland waves after announcing his decision to withdraw from the singles final match against Novak Djokovic of Serbia on day eight of the Barclays ATP World Tour Finals at O2 Arena on November 16, 2014 in London, England. (Photo by Jordan Mansfield/Getty Images)

Getty Images Sport Jordan Mansfield