Defending US Open champion Novak Djokovic complained of feeling "quite rough and unpredictable" as a nagging shoulder problem hampered him during Wednesday's second-round win over Juan Ignacio Londero.
The world number one received medical treatment to his left shoulder throughout the match on his way to a 6-4, 7-6 (7/3), 6-1 win and said he feared the injury could have forced him to retire.
"It was not easy to play with this kind of sensation, to be honest. I did not experience that too many times in my career," Djokovic said.
"I had obviously, you saw, a medical timeout. At changeovers, I tried to use within the rules as much as I can physiotherapy and medical help. That has definitely helped me stay in the match.
"The way it has started for me, especially midway through the first set, I didn't know if I would be able to finish the match."
"I've been experiencing some days of higher intensity of pain, some days less. It has been really fluctuating a lot, going up and down. What happened today on the court, actually how I felt, was quite rough and unpredictable."
- Crucial day off -
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"I'm going to assess this injury tomorrow even more with further consultations with experts in sports medicine. I'm hoping that in two days' time I will be able to play pain-free, if that is possible."
"It wasn't easy to play with the pain, but you have to hope you will get some opportunities and some lucky shots."