Novak Djokovic pulled out of the Western & Southern Open on Monday, meaning the next time he will be in action will be as he tries to complete a calendar-year Grand Slam at the US Open.

The top-ranked Djokovic wrote on social media that he needs “a bit longer to recover and recuperate after quite a taxing journey from Australia to Tokyo.”

He is 21-0 in Grand Slam action in 2021, winning the titles at the Australian Open on hard courts in February, the French Open on clay courts in June and Wimbledon on grass courts in July. No man had even won the first three major tennis championships — let alone all four — in one season since Rod Laver’s true Grand Slam in 1969.

After Wimbledon, Djokovic went to the Tokyo Olympics in pursuit of a Golden Slam — a singles gold medal to go along with all four major trophies in a single season — but he did not manage to collect a medal of any color there.

The 34-year-old from Serbia lost to Germany’s Alexander Zverev in the singles semifinals, then to Spain’s Pablo Carreño Busta in the bronze-medal match.

“I just didn’t deliver yesterday and today. The level of tennis dropped. Also due to exhaustion — mentally and physically,” Djokovic said after the latter defeat. “I gave it all, whatever I had left in the tank, which was not so much.”

Djokovic also lost with partner Nina Stojanovic in the mixed doubles semifinals, then withdrew from that event’s bronze-medal match.

The Western & Southern Open starts next weekend in Cincinnati. The main draw of the US Open begins Aug. 30 in New York.