Rafael Nadal's US Open participation has been called into question by an injury which will force him to wear a cast on his right wrist for up to three weeks.
The world number two won the event last year, beating Novak Djokovic in the final for his 13th major title, to which he has since added this year's French Open.
But he faces a tight schedule to be fit for this year's event, which starts on August 25, after suffering an injury which will prevent him also defending his Rogers Cup and Western and Southern Open titles earlier in the month.
A statement issued by Nadal's representatives B1PR read: "Spanish star Rafa Nadal won't be able to compete and defend his titles from last year in Canada and Cincinnati.
"The player felt some pain during practice in Mallorca getting ready for the North American swing. After some tests today at the Clinica Mapfre de Medicina del Tenis, the doctors found a minor detachment of the posterior cubital tunnel of his right wrist.
"The player must remain for two or three weeks with an immobilisation cast on his right wrist. Depending on the evolution of the injury that will be carefully followed by the doctors, including MRI tests, it will be decided then the return to competition, initially scheduled for the US Open."
The cubital tunnel houses the ulnar nerve, which runs from the elbow to the fingers and is colloquially known as the 'funny bone'.
Wrist injuries have been commonplace in tennis this season, with men's world number eight Juan Martin del Potro undergoing surgery and Laura Robson falling to fourth in the British women's rankings after a similar issue.
While Nadal's injury is to his right wrist, not his dominant hand, his two-handed backhand would still be badly affected.