Defending men's champion Novak Djokovic reportedly had a shoulder issue which bothered him in his second-round match.

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.

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.