LONDON, ENGLAND - NOVEMBER 14: Andy Murray of Great Britain plays a backhand during the mens singles match against Marin Cilic of Croatia on day two of the ATP World Tour Finals at at O2 Arena on November 14, 2016 in London, England. (Photo by Clive Brunskill/Getty Images)

LONDON, ENGLAND - NOVEMBER 14:  Andy Murray of Great Britain plays a backhand during the mens singles match against Marin Cilic of Croatia on day two of the ATP World Tour Finals at at O2 Arena on November 14, 2016 in London, England.  (Photo by Clive Brunskill/Getty Images)