Twelve-time Grand Slam champion Novak Djokovic will not play again in 2017 because of an elbow injury.
Former world number one Djokovic, 30, retired injured during his Wimbledon quarter-final match against Tomas Berdych on 12 July.
He claimed to have been suffering from an elbow problem for 18 months.
"Professionally this is not an easy decision for me, but I'm trying to look at the positive side," said the Serb, who is the world number four.
In July, Djokovic won the Aegon International in Eastbourne - his 68th career title, but his first since January.
He suffered a shock defeat by world number 117 Denis Istomin at January's Australian Open, where he was defending champion, and then lost his French Open crown when he was beaten by Dominic Thiem in the quarter-finals in June.
Djokovic said he would spend the time building up his fitness and strength, as well as working on areas of his game he felt needed to be improved.
"I want to play professional tennis for many years to come," he added in a message on his Facebook page.
It means Djokovic will miss the US Open, which starts on 28 August, and where he was champion in 2011 and 2015.
His absence from Flushing Meadows ends a run of 51 consecutive appearances at Grand Slams.
"All the doctors I've consulted, and all the specialists I have visited, in Serbia and all over the world, have agreed that this injury requires rest," Djokovic said.
"A prolonged break from the sport is inevitable. I'll do whatever it takes to recover.
"My elbow is hurt due to excessive playing, and it troubles me constantly when serving, and now when playing forehand as well.
"My body has its limits, and I have to respect that and be grateful for all I have achieved so far.
"At the beginning of my career I was facing health issues, but over the years, and with a lot of patience and dedication, I found a solution.
"That's the approach I take to this situation, and I firmly believe I will come back stronger."
Coach Andre Agassi has committed to stay with Djokovic for the 2018 season.
BBC Radio 5 live tennis commentator David Law
It has been clear for a while that something had to give.
You get the sense that, after 51 straight Grand Slam tournaments over a 12-and-a-half-year period, his body has simply said 'enough is enough'.
Even his famous resilience and defiance has been lacking of late, suggesting burnout after his extraordinary achievement of holding all four Grand Slam singles title at the same time last year.
A break from the rigours and relentlessness of the game should help in that regard, too.
The good news is that he doesn't need surgery, and he has made his intentions clear by signing up Andre Agassi for 2018, and declaring that he hopes to play for another five years or more.
Exactly a year ago to the day, Roger Federer called time on his 2016 season because of a knee problem. If Djokovic's return goes half as well as Federer's - the Swiss has won the Australian Open and Wimbledon this year - it will certainly have been the right decision.
Rankings-wise, Djokovic will plummet. Federer showed that it doesn't take long to rebuild with the right results early on in a comeback, and Djokovic is nearly six years Federer's junior.
There are also question marks surrounding Andy Murray's health after hip problems over the grass court season, but the suggestion is the world number one may still play the US Open. With Djokovic not there his chances, and those of everyone else, have taken a boost.
Are the recent health issues of Federer, Djokovic, Murray and Nadal a sign of wider issues within the sport - the length of the season, the length of matches?
Perhaps, but the fact is all four are at the top in their 30s, with careers of well over a decade behind them. Many players of the past would have retired by now.