Novak Djokovic, as initially expected, won his US Open second-round match against Juan Ignacio Londero on Wednesday.
But despite the scoreline of 6-4, 7-6(3), 6-1, there could be major concerns for the world No. 1 and defending champion.
Djokovic, with pain in his left shoulder, was in initial trouble against the Argentine.
The 16-time major champion, who had visits from the trainer multiple times, could be seen grimacing early and was shaking out his left arm during the match.
Djokovic said to ESPN on court after the match that the shoulder was affecting his serve and backhand, but he didn't want to elaborate further on the extent of the injury.
"I was definitely tested," Djokovic said to ESPN. "This is something I've been carrying for quite a while now."