The New York Daily News reported the customer, a woman who works for the Wall Street Journal, ordered a salade nicoise at Pret A Manger and was shocked to discover a dead frog among the greens.
Kathryn Lurie, a Wall Street Journal editor, posted a picture of her colleague's aborted meal to social media site Instagram, the New York Post reported.
"She was pretty shaken, understandably," Lurie said of her coworker.
Pret A Manger released a statement saying the incident is under investigation.
"Our lettuce is sourced from farms that do not use any pesticides on its produce, therefore organic matter does very rarely manage to pass through our production process. We are currently looking into this issue to make every effort that this does not happen again," the statement read.