DUBAI, UNITED ARAB EMIRATES - MARCH 01: Roger Federer of Switzerland returns a shot during his second round match against Evgeny Donskoy of Russia on day four of the ATP Dubai Duty Free Tennis Championship on March 1, 2017 in Dubai, United Arab Emirates. (Photo by Tom Dulat/Getty Images)

DUBAI, UNITED ARAB EMIRATES - MARCH 01:  Roger Federer of Switzerland returns a shot during his second round match against Evgeny Donskoy of Russia on day four of the ATP Dubai Duty Free Tennis Championship on March 1, 2017 in Dubai, United Arab Emirates.  (Photo by Tom Dulat/Getty Images)