Kei Nishikori faces a race against time to be fit for this month's U.S. Open after the Japanese world number 11 was ruled out of action for three weeks with a toe injury.
The 24-year-old, the first Japanese to break into the top 10 of the men's singles rankings, received treatment on the big toe of his right foot and would require three weeks to recover, the Kyodo news agency reported on Tuesday.
The injury rules Nishikori out of warm-up tournaments in Toronto and Cincinnati with his management company also unable to confirm his participation in the final major of the year starting on August 25 in New York.
"He will return to the court as soon as possible," the company said in a statement.
The injury-prone Nishikori lost to Briton Daniel Evans in the first round of the U.S. Open last year.
(Reporting by Amlan Chakraborty; Editing by John O'Brien)