CHARLOTTE, North Carolina (AP) — Japan's Kei Nishikori is in doubt for the U.S. Open after he had a cyst removed from his right foot.

Dr. Robert Anderson performed the procedure on Monday in Charlotte, North Carolina. Nishikori's agent, Olivier Van Lindonk, says in an email that his client will fly to his U.S. home in Florida on Tuesday to begin his recovery.

Nishikori, the first Japanese man to reach the top 10 in the rankings, is No. 11 this week. He lost to Richard Gasquet in the quarterfinals in Washington on Friday.

Nishikori will miss next week's tournament in Cincinnati. The U.S. Open begins Aug. 25.