He arrived at Madrid's La Paz hospital on Saturday morning insisting that he had been bitten by what he identified as a diamondback rattlesnake - crotalus atrox – a venomous rattlesnake species found in deserts in southwestern USA and Mexico.
The man, whose identity has not been made public, insisted that he was a snake expert and "by complete chance" had come across the serpent as he walked in a park in the Tetuán district of Madrid.
He told medical staff exactly what antidote was needed, but as the snake is not native to Spain and is forbidden to be kept as a pet, no such anti-venom was in stock.
However, the hospital called on Faunia, a zoo in Madrid that has exotic animals, including rattlesnakes, which keeps the correct antidote in stock in case any of its keepers were bitten.
He told a doctor at the hospital that he had tried to catch and kill the snake to protect the public and was bitten in the process.
"According to his version, he was walking in the park, saw a snake and went to remove it so it couldn't hurt children," Ana Martinez, an emergency doctor at La Paz told Spanish news agency Efe.
“He said he crushed the head of the snake with one foot."
Police who went to search the park found the dead snake, which they described as being a metre in length and confirmed was a rattlesnake and a species that was illegal to be kept as a pet in Spain.
But authorities are suspicious of the bitten man's story and suspect he may in fact be the true owner of the snake, and that he concocted the tale of finding it in the park to avoid prosecution.
He is being investigated for ownership of an illegal animal. The fine for keeping a venomous snake is €20,000.