Kei Nishikori says his injured left calf is healed after taking time off following Wimbledon.
Japan's Nishikori is seeded No. 2 at the Citi Open hard-court tournament and, after a first-round bye, he will face Australia's James Duckworth in the second round on Tuesday.
Nishikori, the runner-up at the U.S. Open in 2014, said Monday he is "feeling pretty well, actually" and that his leg is fine thanks to a week of rest after his early exit at the All England Club in early July.
He withdrew before his second-round match at Wimbledon, citing a lingering problem with the calf. The Citi Open marks his first tournament since then.
Duckworth advanced Monday by beating Ryan Harrison of the United States 6-1, 7-6 (4).