ABU DHABI, UNITED ARAB EMIRATES - DECEMBER 29: Rafael Nadal of Spain reacts during day one of the Mubadala World Tennis Championship at Zayed Sport City on December 29, 2016 in Abu Dhabi, United Arab Emirates. (Photo by Francois Nel/Getty Images)
ABU DHABI, UNITED ARAB EMIRATES - DECEMBER 29: Rafael Nadal of Spain reacts during day one of the Mubadala World Tennis Championship at Zayed Sport City on December 29, 2016 in Abu Dhabi, United Arab Emirates. (Photo by Francois Nel/Getty Images)