Kei Nishikori has pulled out of the Rome Masters, but is excited about his prospects for the French Open after his performance in recent clay events.

Nishikori won Barcelona and then reached the final of the Madrid Masters last week, going up a set and break against Rafael Nadal before retiring with a back injury in the third set. He did not win a game after getting treatment before serving at 4-3 in the second set, and retired three games into the third set.

"It was very tough mentally for me," the 24-year-old said, but added that he has drawn confidence from his recent breakthroughs. His results have made him the first Japanese male to reach the Top 10.

"It's going to be very exciting at the French Open because I've never felt like this on clay," said Nishikori. "I'm very confident of whatever I hit. I'm playing better from last year. I'm playing more aggressive, offensive, playing from both sides, and playing really confident right now."

This is the second time this year Nishikori has gone out of a Masters event with physical problems—he withdrew before the Miami semifinals with a groin injury.

Writing on Facebook, Nishikori said he was returning to Florida to get treatment and prepare for the French Open, which begins in two weeks.