NEW YORK, NY - AUGUST 30: Gael Monfils shakes hands with his opponant Kei Nishikori of Japan after he retires due to an injury on Day Four of the 2018 US Open at the USTA Billie Jean King National Tennis Center on August 30, 2018 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Sarah Stier/Getty Images)
