- Tag results for Rafael Nadal
Nadal had to pull out during his semi-final against Juan Martin del Potro in New York and also missed Spain's Davis Cup defeat by France last weekend.
Rafael Nadal continued to lead the rankings despite his forced retirement at the US Open over a knee injury.
Seeded to face Federer in the quarter-finals, Djokovic found himself instead across the net from John Millman after the unheralded Australian stunned the Swiss great.
Nadal will be replaced by world number 52 Albert Ramos-Vinolas for the September 14-16 clash against the defending champions as Spain attempt to reach their first final since 2012.
Djokovic will start the heavy favourite, boasting a 14-4 record over the Argentine who will be playing in just his second final at the Slams.
US Open finalist Juan Martin Del Potro is the next in line to qualify for the 2018 Nitto ATP Finals, which would mark his first appearance at The O2 in London since 2013.
The Spaniard, his world number one ranking still safe, said the trouble was the familiar tendinitis he's dealt with for a decade -- unpredictable but not career-threatening.
The Spaniard twice needed to have his right knee bandaged before calling it a day after the conclusion of the second set.
Defending champion Rafael Nadal survived an epic US Open quarter-final confrontation to defeat battling ninth seed Dominic Thiem 0-6, 6-4, 7-5, 6-7 (4/7), 7-6 (7/5).
World number one Nadal saw off a battling Nikoloz Basilashvili, the first Georgian in a fourth round in New York, 6-3, 6-3, 6-7 (6/8), 6-4.
Nadal's knee was bothering him. His decade-younger, barrel-chested US Open foe was bashing the ball.
Rafael Nadal said that he saw no reason the tournament couldn't limit what players wear, noting that Wimbledon did the same with its insistence on white.
David Ferrer called it quits on a hot and humid night on Arthur Ashe Stadium when he led 4-3 with a break in the second set.
For the first time since Wimbledon in June 2017, a tournament will have the entire Big Four in the field: Roger Federer, Rafael Nadal, Novak Djokovic and Andy Murray.
Rafael Nadal and Serena Williams, the two superstars, who own 40 Grand Slam titles between them, headline an opening day that sees eight former US Open champions in action.