Kei Nishikori's 2017 season is over due to a torn tendon in his right wrist.
The Japanese joins Novak Djokovic and Stan Wawrinka in calling a premature end to his schedule for the year, while Andy Murray - soon to be replaced as world number one by Rafael Nadal - and Roger Federer also have fitness concerns.
Nishikori, ranked ninth in the world, lost to Gael Monfils in the second round of the Rogers Cup last week and will not have the chance to better his run to the semi-finals at the US Open last year.
"Two days ago during practice in Cincinnati, Kei hit a serve and heard a 'pop' in his wrist," his manager said in a statement on Wednesday, as quoted by the US Open website.
"We went straight to the hospital to take an MRI. Yesterday, we went to see a very renowned wrist specialist who works with many of the MLB baseball pitchers.
"We saw another specialist today to get a second opinion. On top of that we have sent MRI results to three other wrist specialists to ensure we get several independent opinions from specialists.
"After consulting with all of them, it has become clear that Kei has a tear in one of the tendons in the right wrist.
"At this stage we have elected not to do surgery and Kei is in a cast. After the swelling comes down in the next weeks, we will evaluate next steps. Kei will withdraw from all the 2017 tournaments and work hard to be ready for next year."
Nishikori will end the year without a title, with his best grand slam outing this year coming at the French Open, where the 27-year-old reached the last eight.
After Nishikori's withdrawal from the Western and Southern Open, lucky loser Janko Tipsarevic was added to the Cincinnati draw.