The horrified customer spat out the 4-inch long amphibian, but is worried that he may have eaten one of its legs.
Accounts manager Ross Dance said: “I bit into the wrap, but couldn’t chew through it. I excused myself and got it out of my mouth.
“There was a whole frog there. It was still alive. I felt really ill.”
Dance, 32, found the then three-limbed animal at the restaurant chain’s branch in Victoria, central London, and insisted on taking it home in a plastic tub.
Dance, from Crawley in West Sussex, added: “I think I might have eaten one. The thought of chewing on it keeps me awake at night.
“I don’t understand how anyone can put a wrap together and not see a frog. I’m livid. I won’t eat at Nando’s again.”
The South African food firm Nando’s, who gave Dance a £44 refund, said it was taking the incident seriously.
It said the frog must have hopped into washed and ready to eat salad leaves, which are pre-packed and provided by a supplier.
A spokesman said: “We take great care over the quality of our food.
“Unfortunately as Mr Dance refuses to give us the foreign object, we are unable to fully understand where it came from to reach a final conclusion.”
Customers have taken their shock to Twitter, with @SweetGirlNokz saying: “Nandos is a mess.”
The fast-food restaurant also caused controversy this month in Zimbabwe with an advert mocking President Robert Mugabe.