Three-time champion Novak Djokovic is the only member of the "Big Three" in the field for the 2020 U.S. Open.

Roger Federer said previously he will miss the Aug. 31-Sept. 13 tournament in New York while recovering from knee surgery, while Rafael Nadal said he is skipping the Grand Slam event due to the ongoing COVID-19 pandemic.

The U.S. Tennis Association announced the entry list for the tournament on Tuesday.

Djokovic, who won U.S. Open singles titles in 2011, 2015 and 2018, is attempting to win his 18th Grand Slam. The 33-year-old Serbian is ranked No. 1 in the world and was riding an 18-match unbeaten streak when the ATP Tour was suspended due to the coronavirus in March.

Nadal, the world No. 2, posted a series of tweets Tuesday explaining his decision not to defend his U.S. Open title. He also won the event in 2010, 2013 and 2017.

"After many thoughts I have decided not to play this year's US Open. The situation is very complicated worldwide, the COVID-19 cases are increasing, it looks like we still don't have control of it," he wrote. "... This is a decision I never wanted to take but I have decided to follow my heart this time and for the time being I rather not travel."

With the 38-year-old Federer (a five-time U.S. Open champ) and Nadal out of the field, younger stars like Dominic Thiem, Daniil Medvedev, Stefanos Tsitsipas and Alexander Zverev will look to make their Grand Slam breakthroughs.

Others entered in the main draw at Flushing Meadows include 2019 semifinalists Matteo Berrettini and Grigor Dimitrov, 2014 champion Marin Cilic and former finalists Kei Nishikori (2014) and Kevin Anderson (2017).

Either Djokovic, Nadal or Federer have won the 13 Grand Slam tournaments since Stan Wawrinka of Switzerland was victorious in the 2016 U.S. Open.