LONDON, ENGLAND - NOVEMBER 12:  (L- R) Kei Nishikori of Japan, Novak Djokovic of Serbia, Andy Murray of Great Britain, Roger Federer of Switzerland, Stan Wawrinka of Switzerland, Rafael Nadal of Spain, Tomas Berdych of Czech Republic and David Ferrer of Spain pose for a group photo during the Barclays ATP World Tour Finals Draw at City Hall on November 12, 2015 in London, England.  (Photo by Julian Finney/Getty Images)