Kei Nishikori bowed out of the Delray Beach Open on Thursday, when he retired from his second-round match due to injury.
Nishikori, ranked 15th in the world and the third seed here, was trailing 4-2 in the first set against 65th-ranked Teymuraz Gabashvili of Russia, when he retired after suffering from pain in his left leg.
"Against this caliber of opponent, you can't win if you're not 100 percent," said Nishikori, who was seeking his fifth career ATP title after defending his U.S. National Indoor Tennis Championships crown on Sunday.
"I'm not that concerned about this. Because it's probably just muscle pain, I think I'll just need rest and some treatment."
Nishikori revealed he had felt some groin pain during practice before his first-round match and had considered retiring then.
"During that match, too, I was conflicted about what to do," he said.
Last year, Nishikori withdrew from his first-round match at Delray Beach due to pain in left oblique muscles. Although he has dealt with a variety of injuries, this one appears to be a new one and he is going to undergo an examination in the coming days.
"I don't want to get down about it," he said. "Instead, I want to heal and come back fresh."
According to an ATP source, Nishikori has already withdrawn from next week's Abierto Mexicano Telcel in Acapulco.