The birds can kill humans and other animals with their huge talons capable of ripping open flesh.
The Alachua County Fire Rescue Department said it appeared the man had fallen and was attacked by the bird with its long claws.
Police added that the cassowary involved in the attack "remains secured on private property".
The San Diego Zoo's website calls them the world's most risky bird with a four-inch (10-centimeter), dagger-like claw on each foot that can cut open people or predators.
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"My understanding is that the gentleman was in the vicinity of the bird and at some point fell", he said.
"It looks like it was accidental", Taylor said.
Southern cassowaries, the most well-known of the three cassowary species, can measure between 4 and 5.6 feet tall, with females weighing in at up to 167 pounds, according to the San Diego Zoo. "Powerful legs help the cassowary run up to 31 miles per hour (50 kph) through the dense forest underbrush", AP quoted the website as explaining.
Parts of the cassowaries are eaten in New Guinea, but breeders in the United States do not raise cassowaries for food. The birds are sought after in the United States by collectors of exotic birds.
"Substantial experience and specific cage requirements must be met" for a permit to be issued for handling these types of animals, FWC spokeswoman Karen Parker said.
Wildlife officials did not answer phone calls late Saturday from The Associated Press and it wasn't immediately known what would happen with the bird.