World number one Novak Djokovic insists his arm is "all good" despite needing treatment during his first-round win over Jerzy Janowicz at the US Open.
The Serbian defending champion was below his best in a 6-3 5-7 6-2 6-1 victory over Pole Janowicz at Arthur Ashe Stadium on Monday.
Djokovic, a 12-time grand slam winner, took a medical timeout midway through the first set to receive treatment on his right arm.
He came into the year's last grand slam with a wrist injury, but said his fitness was slowly improving.
"It's getting better and better each day. I'm glad that I'm experiencing that," Djokovic said.
"So hopefully as the tournament progresses, I'll reach my peak."
As for the treatment he received on his arm, Djokovic said: "It was just prevention. It's all good."
Awaiting Djokovic in the second round is Czech Jiri Vesely, who won their only previous meeting earlier this year.
Djokovic's wrist injury, and personal problems which impacted his Wimbledon campaign, have seen expectations played down, but he hopes gradual improvement in his health can help him to success.
"To be honest, I take it day by day. That's what I feel at the moment. It's good, as I said, just to finish the match," he said.
"I'm pleased that as the match progressed I was feeling better and better.
"Tomorrow is a new day. I hope that I'll feel overall good so I'm able to perform at my best for the next match."