Britain's Kyle Edmund will miss next month's Australian Open because of a persistent knee injury.
World number 48 Edmund was a semi-finalist in Melbourne in 2018.
However, the British number two had to end his 2018 season early after a scan revealed fluid behind his knee and then retired from his second-round match at the 2019 French Open with a knee issue.
"Unfortunately, my knee is not quite ready to compete in the upcoming Australia swing," said the 26-year-old.
"I hope to be back competing soon."
Since the sport returned after lockdown, Edmund has won only one of his seven matches, beating Alexander Bublik of Kazahkstan in the opening round of the US Open before losing to top seed Novak Djokovic.
The Australian Open, the first Grand Slam of the year, is due to start on 8 February after being delayed for three weeks because of the Covid-19 pandemic.
Analysis
BBC tennis correspondent Russell Fuller
The first evidence of what has become a chronic knee problem was when Edmund pulled out of the 2018 Paris Masters following a scan which revealed fluid behind his left knee.
The timing could not have been worse, as earlier that year Edmund has reached the semi-finals of the Australian Open, won his first ATP tournament in Antwerp, and climbed to 14 in the world.
The injury also affected him in the summer of 2019, when he had to retire from his second-round match at Roland Garros. He would go on later that year to lose eight matches in a row.
He did win a second title in New York early last year, just before the tour went into hibernation, but the going has been tough ever since.
The frustration must be immense given that, at 26, Edmund should now be entering the best years of his career.