Novak Djokovic pulled from the Western & Southern Open on Monday. He will now be trying to complete a calendar year Grand Slam at The US Open.Djokovic, the top-ranked tennis player, posted on social media that it took him a while to recuperate from the long and tiring trip from Australia to Tokyo.In Grand Slam action, he is now 21-0. He won 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. Since Rod Laver's 1969 true Grand Slam, no man had ever won any of the three major tennis championships.Djokovic was determined to win a Golden Slam at the Tokyo Olympics. This is a singles gold and doubles medal that can be added to all four major trophies. However, he failed to capture any medal of any color.The 34-year old from Serbia lost to Alexander Zverev, a German singles semifinalist, and then to Pablo Carreo Busta, a Spaniard in the bronze-medal match."I didn't deliver yesterday or today. The level of tennis has dropped. Djokovic stated that the loss was also due to exhaustion, both mentally and physically. "I gave everything I had in the tank. It was not enough."Djokovic lost the semifinals of mixed doubles with Nina Stojanovic, and then pulled out from the bronze-medal match.Next weekend, the Western & Southern Open will begin in Cincinnati. The US Open's main draw begins August 30th in New York.Djokovic won the Western & Southern Open title last year. The tournament was played at Flushing Meadows (the site of the US Open) as part of a back-to-back staging during the coronavirus pandemic.Monday's post by Djokovic stated that he would "turn my attention to the US Open and spend more time with my family." We look forward to seeing you in New York!Djokovic will also be trying for his fourth one-year Slam title by a male -- Laver did it twice during the 1960s, Don Budge did it in 1930s -- and he will also be trying to win his 21st major career title at the US Open. He would be breaking the 20-year men's record he shares with Roger Federer, Rafael Nadal and others.