LONDON, ENGLAND - NOVEMBER 17: Roger Federer of Switzerland hits a return against Alexander Zverev of Germany during Day Seven of the Nitto ATP Finals at The O2 Arena on November 17, 2018 in London, England. (Photo by Fred Lee/Getty Images)
LONDON, ENGLAND - NOVEMBER 17: Roger Federer of Switzerland hits a return against Alexander Zverev of Germany during Day Seven of the Nitto ATP Finals at The O2 Arena on November 17, 2018 in London, England. (Photo by Fred Lee/Getty Images)