The panther chameleon was found on Monday by a dog walker in the wooded area at Marl Park.
It had to be put down after X-rays showed all of its legs were broken and it had a deformed spine.
RSPCA Cymru said it was an "extremely sad example of an abandoned and neglected exotic pet".
Inspector Selina Chan said: "It is a possibility that the owners took on this animal but were unable to provide the care he needs and decided to release him to the wild.
"We are urging potential owners of exotic animals to thoroughly research what is required in the care of the particular species before taking one on.
"Potential owners need to make sure they can give their animal the environment it needs and they have the facilities, time, financial means and long-term commitment to maintain a good standard of care, as required under the Animal Welfare Act 2006."
She added it was illegal to release non-native species into the wild.
Owners of exotic animals have been urged to do research before having them as pets after a seriously neglected chameleon was found in Cardiff Bay.