Defending champion Dominic Thiem will miss the US Open and the rest of the season after failing to recover from a wrist injury.
The 27-year-old Austrian hurt himself at the Mallorca Open in June and has been off the tour since.
“I’m really disappointed not to be able to defend the title in New York,” he said on Twitter on Wednesday.
“It has been a tough decision to make, but I know this is what I have to do.”
The US Open starts on Aug. 30.
Thiem’s comeback five-set victory over Alexander Zverev last year at Flushing Meadows was his first grand slam singles title.
Roger Federer is also out of this year’s US Open, while Rafael Nadal has also been struggling with injury.
Thiem will also miss the ATP Finals’ end-of-season showdown in November, where he was the beaten finalist the previous two years.