RIO DE JANEIRO (AFP) - Spanish tennis stars Rafael Nadal and David Ferrer on Monday insisted that they were not worried by Brazil's Zika virus outbreak as they prepare to compete at the Rio Open ATP tournament this week.

"I'm not at all afraid," Nadal, 29, told a press conference. "I go out at night, and I know there's a risk, but I'm just happy to be back here again.

"If I get sick, well, then that's just bad luck," insisted the 14-time Grand Slam winner.

"I can see for myself that people here are going about their business as if everything was okay, so things can't be that bad.

"People are going to the beach, going out for walks, having dinner in restaurants," the world No. 5 continued.

Ferrer, ranked sixth in the world, said he had been reassured by Brazil's efforts to wipe out the mosquitoes which carry the virus.

"We've been told that everything possible has been done so that there will be no mosquitoes, which is comforting," he said. "We've been wearing long trousers at night but I'm not getting obsessed by the whole thing."

Brazil has been most affected by the outbreak that has spread rapidly through Latin America and the Caribbean, with 1.5 million people in the country infected since early 2015.

While it causes only mild flu-like symptoms in most people, scientists suspect when it strikes a pregnant woman, it can cause her baby to be born with microcephaly, or an abnormally small head.

"The whole thing seems to have been blown out of proportion," Nadal said. "The reality is that we are here in Rio for an international tennis tournament and I'm here and I can see that everything looks totally normal."

Brazil President Dilma Rousseff on Saturday vowed that the virus would not jeopardise the Rio Olympics in August.