Kei Nishikori believes he is physically and mentally ready to contend for a Grand Slam title. The 2014 U.S. Open finalist, who is based at the IMG Academy in Bradenton, Fla., credits American eating habits with helping him bulk up when he was younger. The 25-year-old moved away from Japan as a teenager and has spoken about his difficulties adjusting to his new home.

"I used to eat McDonald's, I had to eat something so I had no choice," he said, speaking to British press in Rome. "I think it was good that I went to the U.S., because after a couple of years, I got much bigger in height and more weight. The taste wasn't the best, but it was good for me, good for the body. Japanese food is healthy but it doesn't get you much bigger."

Despite frequent injuries when he first came on tour, Nishikori has now improved physically. At last year's U.S. Open, he played back-to-back five-setters before defeating Novak Djokovic in the semifinals. "I couldn't really see how I could play two weeks in a row, especially five sets. But after that I was really confident with my physical side and also I was playing amazing the last couple of matches, beating Stan [Wawrinka], beating [Novak] Djokovic. ''

"I think now I am more calm in matches, I don't have too many ups and downs," he said, adding that his coaches, including former No. 2 and French Open champion Michael Chang, have helped him. "I kind of know when I have to raise my level."

Though he is a huge figure in his native country and intends to move back to Japan following his career, Nishikori also suggested that being based elsewhere helps him keep his off-court life calm. "If I stayed in Japan for sure I would get cocky and go crazy, but luckily I am staying in the U.S., so that's why I can concentrate all the time, play tennis and do training, all the important stuff."

Nishikori reached the semifinals of last week's Rome Masters, falling to Djokovic. He's ranked No. 6 going into the French Open.