First level defending champion Novak Djokovic said "life goes on" after a shoulder injury forced him to abandon Sunday's clash with Stan Wawrinka in the last 16 of the US Open.
Wawrinka, the 23rd champion and 2016 champion, led Djokovic 6-4, 7-5, 2-1 when the Serb resigned with a persistent left shoulder problem that had worried him since the start of the tournament.
"The pain was constant for weeks. Some days higher, some days with less intensity and obviously taking different things to kill the pain instantly," Djokovic said.
"Sometimes it works. Sometimes it doesn't. You just know when you know, I guess, when you feel you can't shoot anymore."
Djokovic refused to expand the nature of his injury, which caused him considerable pain during the second round victory over Juan Ignacio Londero.
"I withdrew and told you it was the left shoulder. I have nothing more to talk about," he said.
"I don't want to talk about my injuries. I said it in the past. I'll stick to that."
Djokovic had claimed that he felt "almost painless" after a two-set defeat by Denis Kudla in the third round, but the problem resurfaced against Wawrinka in the first match between the couple since the final here three years ago.
The world number one received treatment before the start of the third set against Wawrinka, but soon threw in the towel, the sixth time he retired in a Grand Slam tournament.
"It's frustrating. Very frustrating. He is obviously not the first, nor the last player to be injured and withdraws from one of the most important events in the sport," he said. "But obviously I just left the court, so, of course, it hurts."
"Obviously I am in the middle of an unfortunate situation, and I have to, you know, suffer the consequences of that. And as I said, I am not the first or the last. Life goes on."
& # 39; Long way ahead & # 39;
But Djokovic, winner of four of Slam's last five events and 16 overall, was optimistic about his chances of catching and beating rival Roger Federer, who holds the men's record for 20 major titles.
"It is no secret that, of course, I desire and I have the goal of reaching as many Slams as possible and achieving Roger's record," Djokovic said.
"But at the same time, it's a long road ahead, I hope to play for many more years. I'm planning to do it. I don't see an end behind the corner at all."
"Now it is about keeping my body and mind in shape and trying to reach the maximum in this type of events that are bigger and that are the most important in our sport."
It was the second time in the last decade that Djokovic retired from a Grand Slam match, having retired for the last time during the quarterfinals of Wimbledon 2017 against Tomas Berdych with an elbow injury.
That setback led him to close it for the rest of the season and generated questions about his future. His spectacular return to form 12 months later silenced those concerns, and he hopes for a speedy recovery.
"This season is not over yet," he said, reflecting on a year in which he added another Australian and Wimbledon Open title to his collection.
"Obviously the Grand Slam season is over for me. I mean, I won two Slams of four and played semifinals in French. I had a very good Grand Slam season. I can't complain at all."
"There are many big tournaments ahead. As for the rankings, many points to defend and try to retain that number one ranking."
"I just hope to have the opportunity to compete, because once I'm healthy I like my chances playing in Asia. And also in the indoor season, I play historically quite well in the last two months of the year."