LONDON, ENGLAND - NOVEMBER 08: Kei Nishikori of Japan in practice with his coach Michael Chang during the Barclays ATP World Tour Finals tennis previews at the O2 Arena on November 8, 2014 in London, England. (Photo by Clive Brunskill/Getty Images)
LONDON, ENGLAND - NOVEMBER 08: Kei Nishikori of Japan in practice with his coach Michael Chang during the Barclays ATP World Tour Finals tennis previews at the O2 Arena on November 8, 2014 in London, England. (Photo by Clive Brunskill/Getty Images)