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SHANGHAI, CHINA - OCTOBER 11: Juan Martin del Potro of Argentina walks off the court after he is forced to retire due to injury against Borna Coric of Croatia during third round of the 2018 Rolex Shanghai Masters match on Day 5 at Qi Zhong Tennis Centre on October 11, 2018 in Shanghai, China.(Photo by Fred Lee/Getty Images)

SHANGHAI, CHINA - OCTOBER 11:  
Juan Martin del Potro of Argentina walks off the court after he is forced to retire due to injury against Borna Coric of Croatia during third round of the 2018 Rolex Shanghai Masters match on Day 5 at Qi Zhong Tennis Centre on October 11, 2018 in Shanghai, China.(Photo by Fred Lee/Getty Images)