Kei Nishikori pulls out of Toronto with infected toe
Kei Nishikori of Japan returns a shot to Richard Gasquet of France during the Citi Open at the William H.G. FitzGerald Tennis Center on August 1, 2014 in Washington - by Rob Carr
Nishikori, ranked 11th, lost to France's 14th-ranked Richard Gasquet in the ATP Washington quarter-finals on Friday.
The Asian number one struggled at times in moving across the court against Gasquet, a US Open semi-finalist last year, but insisted after the match that there was no health problem.
"I'm fine," he said. "He just played well."
Nishikori, who was hoping for a strong US hardcourt season in the run-up to the US Open, must now look to the Cincinnati Masters tournament in two weeks in what figures to be his final warm-up event before the year's final Grand Slam event begins at Flushing Meadows on August 25.
Nishikori lost in the first round at last year's US Open.
This year, Nishikori is enjoying his best season with titles at Memphis and Barcelona.