Rafael Nadal talks tennis, fishing ahead of the US Open

When it comes to diets, many professional tennis players follow rigorous, scientific programs that include calorie counting and nutritional balance. But Rafael Nadal, the world's No. 5 tennis player, likes to keep his meal plans simple.

"It's nothing very professional," he told CNBC from the Taste of Tennis culinary event in New York City Thursday. "Fish is my favorite, grilled with olive oil. And I try to have some carbs, maybe pasta or rice. I try to eat nothing heavy before competition."

Nadal, who grew up in Majorca, Spain, said his favorite meal is one he catches himself.

"I love fishing and being in the sea with boats," he said. "I normally go with lines or spear-guns. I love sea bass. It's great when you are on the boat and catch a sea bass, and have dinner with it."

Nadal's latest sponsor, Olive Oils from Spain, is also a big part of his daily diet — and guilty pleasures.

"I love eating olives," he said. "They're healthy but maybe not if you eat as much as me. And I like chocolate."

Fresh off his gold medal win at the Rio Olympics for men's doubles, Nadal also talked about his excitement for next week's U.S. Open and his recovery from an injury to his left wrist.

"I feel great," he told the crowd Thursday. "There is nothing like the U.S. Open."

Despite there being no American men ranked in the top 10, U.S. tournaments remain popular, Nadal said.

"I think we are in a great moment," he said. "The sport is growing a lot, we have a lot of sponsors, the tournaments are bigger, [and] that's a great thing."