Rafael Nadal will not defend his title at the US Open because of an injured right wrist.
Nadal and the tournament announced his withdrawal on Monday, a week before the year's last Grand Slam tournament begins.
The 27-year-old Spaniard was hurt July 29 while practicing on his home island of Mallorca ahead of the North American hard-court circuit. The next day, Nadal said he had been told by doctors to wear a cast on his wrist for two to three weeks, and would have to sit out US Open tuneup tournaments in Toronto and Cincinnati.
Nadal also said at that time he expected to be able to return for the US Open. But on Monday, he issued a statement on his Facebook page, saying he is "very sorry to announce" he was out of the tournament.
"I am sure you understand that it is a very tough moment for me since it is a tournament I love and where I have great memories from fans, the night matches, so many things," Nadal's posting read. "Not much more I can do right now, other than accept the situation and, as always in my case, work hard in order to be able to compete at the highest level once I am back."
It's only the fourth time in the Open era, which began in 1968, that the reigning US Open men's champion did not return to the field the following year. The others were Ken Rosewall in 1971, Pete Sampras in 2003 and Juan Martin del Potro in 2010.
The second-ranked Nadal plays left-handed, but he uses a two-handed backhand.
Nadal won his second championship at Flushing Meadows in 2013, part of a run of reaching the final in each of his last three appearances in the US Open. He beat Novak Djokovic to win the titles in 2010 and last year, and lost to Djokovic in 2011.
But now he'll be missing the tournament for the second time in three years. Nadal did not enter the US Open in 2012, part of an extended absence because of a problem with his left knee.