Defending champion Dominic Thiem has withdrawn from this year's US Open and will miss the rest of the season.
Thiem has failed to recover from a wrist injury suffered while contesting the Mallorca Open in June.
In a statement, the 27-year-old Austrian said: "Having spent a week training on court, I still felt pain in my wrist and I knew that it was not 100 per cent.
"I went to see my doctors again and we have decided to follow a conservative treatment, giving the injury more time to recover. I'm very disappointed not to be able to defend my US Open title and to miss the rest of the season.
"But I know this is what I have to do. I have a long career ahead of me, so I will only come back once I'm fully recovered and in good shape to compete."