According to media reports, shortly before the Sunday match against Swiss competitor Stan Wawrinka, Djokovic looked fit. The defending champion, however, stopped playing in the fourth round because of the injury, after dropping the first two sets.
The 2016 champion Wawrinka led Djokovic 6-4, 7-5, 2-1 when the Serb quit, having received treatment on his troublesome left shoulder before the start of the third set.
#USOpen— The Field (@thefield_in) September 2, 2019
The 2016 champion marches onto quarters as Novak Djokovic retires.
Stan Wawrinka lead 6-4, 7-5, 2-1 (ret.) and will now face 5th seed Daniil Medvedev for a place in the semi-finals. pic.twitter.com/7Dmq8jnhcb
According to media reports, Djokovic - the No. 1 seed - was in visible pain throughout the whole game. It is the first time Djokovic, a three-time champion, has lost before the semifinal stage of the tournament since 2006, when he was 19.