A source close to the case confirmed after an autopsy was carried out on her body on Friday afternoon that the 33-year-old died from natural causes.
Speaking after his quarter-final victory over Switzerland`s Stanislas Wawrinka at the Shanghai Masters, Nadal said it was "very bad news for the world of sport in general, for Spanish sport especially".
"It`s very difficult to say things on day like today," he said. "Stay positive. All the best for her family. Very difficult to find a word because is a very sad, sad day for all of us.
"I hope she didn`t suffer in that last moment, that`s the only positive thing I think. The rest of the things are all very, very negative. Very, very sad."
De Villota was in the Andalusian city to take part in a conference organised by the "What Really Matters" foundation promoting human values and was due to launch her book titled "Life is a gift" in Madrid on Monday.
The daughter of former Formula 1 driver Emilio De Villota, she was the first Spanish female to enter the sport when she joined the Marussia team in 2012 as a test driver.
However, just four months later De Villota suffered severe injuries, including the loss of her right eye in a crash while testing at Duxford Airfield in Cambridgeshire, England.
First Published: Saturday, October 12, 2013, 10:52