Alexei Popyrin withdrew from the U.S. Open on Sunday, allowing 2012 champion Andy Murray to move into the main draw. 

That means Murray can relinquish the wild-card invitation he received from the U.S. Tennis Association, which now will be given to American Mitchell Krueger. 

Popyrin, the 21-year-old Australian, joins Australians world No. 1 Ashleigh Barty and Nick Kyrgios as players who are skipping the race.  

Former champion 35-year-old Swiss Stan Wawrinka also confirmed that he would not play the U.S. Open citing "the health situation in New York" as the Grand Slam event took another hit. 

The women's draw has also lost other top-10 players including No. 5 Elina Svitolina and seventh-ranked Kiki Bertens due to their concerns about the pandemic. 

Meanwhile, World No. 2 Simona Halep said she would take the final decision on her participation in the U.S. Open after playing this week's WTA Tour event in Prague. 

Twenty-three-time Grand Slam champion Serena Williams, 38, has committed to playing in the event. 

Dominic Thiem says U.S. Open will be "worth much less" 

World No. 3 Austrian Dominic Thiem will be at Flushing Meadows, but he suggested the upcoming event will be "worth much less" due to the number of top-flight players giving the tournament a miss. 

"You have to be honest and keep in mind that many top players will not attend the tournament. That means going far in this tournament it would be worth much less than normal compared to the Australian Open this year."

Players at the U.S. Open, which starts on August 31 to September 13, will be subject to tight health controls to avoid the spread of the coronavirus. It is scheduled to be played without spectators in New York. 

(With input from agencies)