Kei Nishikori is out for the rest of the season after
tearing a tendon in his right wrist.
The world number nine joins 12-time Grand Slam champion Novak Djokovic
and Stan Wawrinka in missing the US Open, which starts on 28 August.
Nishikori, 27, is also one of seven top-10 players to pull out of this week's Cincinnati Masters.
"
Kei hit a serve during practice and heard a 'pop' in his wrist," said a statement from his manager.
"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."
Djokovic, Wawrinka, Andy Murray, Roger Federer, Marin Cilic
and Milos Raonic are the other top players missing in Cincinnati.
bbc news today 
Kei Nishikori : World number nine will miss the rest of the season after injury
The world number nine joins 12-time Grand Slam champion Novak Djokovic
and Stan Wawrinka in missing the US Open, which starts on 28 August.
Nishikori, 27, is also one of seven top-10 players to pull out of this week's Cincinnati Masters.
"Kei hit a serve during practice and heard a 'pop' in his wrist," said a statement from his manager.
"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."
Djokovic, Wawrinka, Andy Murray, Roger Federer, Marin Cilic
and Milos Raonic are the other top players missing in Cincinnati.
bbc news today