He announced his decision on his website and Facebook:
“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. A prolonged break from the sport is inevitable. I’ll do whatever it takes to recover. I will use the upcoming period to strengthen my body and also to improve certain tennis elements that I have not been able to work on over the past years, due to a demanding schedule. Five months may seem long from this point, but I’m sure they will pass quickly because there is so much I want to do. Another important moment is coming, we will become parents for a second time. My wife Jelena and I are expecting our second child, and we are preparing to welcome a new family member. These are things that fill me with greatest happiness and delight. I’m confident I will be ready for start of the new season."This means that Djokovic's streak of 51-consecutive majors played will end and he will miss the 2017 US Open where he has played in the final 6 of the last 7 years (winning twice: in 2015 d. Federer and 2011 d. Nadal).
World #1 Andy Murray is also expected to possibly curtail his season (presumably after the US Open) and cede the race to the ear-end #1 to a thrilling battle between Federer and Nadal. It also means that Federer is now probably the prohibitive favorite for the 2017 US Open, and the chances of a Federer-Nadal match at that tournament (which has never happened) increase.