New York City is among the cities worst hit in the USA by the pandemic, which has claimed the lives of over 150,000 Americans, but the tournament is set to go ahead as originally scheduled on August 31.
"My team and I have decided that we won't be travelling to the U.S. for the Western and Southern Open and the US Open this year," the Australian said in a statement issued by her manager on Thursday.
"I love both events so it was a difficult decision but there are still significant risks involved due to Covid-19 and I don't feel comfortable putting my team and I in that position.
"I wish the USTA all the best for the tournaments and look forward to being back in the US next year."
The Western and Southern Open, which is held annually in Cincinnati, has been moved to New York this year and is set to start in mid-August.
Coaching Roger Federer and Novak Djokovic - Wimbledon special of Tennis Legends
The reigning French Open champion will decide later whether to defend her title at Roland Garros starting in late September.
"I will make my decision on the French Open and the surrounding WTA European tournaments in the coming weeks," she said.
World number one Novak Djokovic and 23-times Grand Slam champion Serena Williams are among players expected to compete at the U.S. Open despite concerns about undergoing mandatory quarantine when travelling to Europe, which would have them miss tournaments in Madrid and Rome ahead of the French Open.
Deaths from Covid-19 surpassed 150,000 in the United States on Wednesday, more than any other country and nearly a quarter of the world's total, according to a Reuters tally.