Serena Williams was included on the entry list for the U.S. Open on Wednesday as was Novak Djokovic even though his refusal to be vaccinated will bar him from entering the country. 

Williams, who won the first of her six New York titles in 1999, remains frustratingly one Grand Slam short of Margaret Court's record of 24. 

The American star won the last of her 23 majors at the 2017 Australian Open while pregnant. Her most recent U.S. Open title triumph was in 2014.

Former World No.1 Williams only returned to singles action at Wimbledon last month after a year on the sidelines injured.

Djokovic, fresh from capturing his seventh Wimbledon title and 21st major, is on the list for the August 29 to September 11 tournament, the season's final Slam event. 

The three-time winner will, however, be unable to enter the United States after refusing to be vaccinated against COVID-19.

"The U.S. Open does not have a vaccination mandate in place for players, but it will respect the US government's position regarding travel into the country for unvaccinated non-US citizens," said a statement by the United States Tennis Association (USTA).  

Almost 12,000 people have signed an online petition calling for the USTA to work with the country's government to allow Djokovic to compete.

Meanwhile, men's World No.1 Daniil Medvedev returns to defend his title. 

Medvedev and his fellow Russians were banned from Wimbledon this year, but can play in New York without under their national flag. 

Women's champion Emma Raducanu and Japan's four-time Grand Slam title winner Naomi Osaka are also on the entry list. 

Belgian tennis coach Wim Fissette said on Wednesday he was calling a halt to working with former World No. 1 Osaka, who has slipped to 84 in the rankings and has not played since a first round exit at the French Open in May.

(With input from agencies)