Djokovic will still have the chance to capture the calendar Grand Slam, making him the first male player in the Open Era to do so and the first man since Rod Laver in 1969.
Having already won the Australian Open, Roland Garros and Wimbledon, the top-ranked player would only need to secure the US Open crown in a few weeks’ time to complete the set.
His long-time rival Nadal has already said he has “no doubt” the 34-year-old can win all four Majors.
Speaking in Washington, where he is playing his first tournament since the French Open, he said: “He’s already won three, so when you win three, you can win four, without a doubt.
“He’s going to be playing on hard courts, probably his best surface, so why not?”