The surprised shopper called authorities concerned about the frog’s injured leg it suffered on its mammoth journey in a bunch of bananas to Sheen, south London.
Philip Norman, of the RSPCA, responded to the call out to check on the 3cm frog which miraculously survived being “wrapped up in the bag for some time”.
He said: “The shopper had bought them at a local supermarket but had quite the shock when he unwrapped them at home to find the little frog inside.
“The bananas had come from the Dominican Republic so this little one had quite the adventure!”
The frog is thought to be either a Hispaniolan common tree frog or a Dominican tree frog.
It had an injured leg and was taken to the Heathrow Animal Reception Centre where it is recovering.
It came months after another frog called Minty took a 6,000-mile trip from Africa to Northumberland in a bag of fresh mint.
He was discovered after being sold by a fruit and vegetable store hidden in a sealed bag of the leaves imported from Ethiopia.
The frog is being cared for by RSPCA inspector Lucy Green at home in her tropical tank as she tries to establish what species he is.
The RSPCA urged Londoners to visit their website or call their donation line on 0300 123 8181 to continue rescuing, rehabilitating and rehoming animals in need.