The proteins make the skin transparent and give off a greenish glow when exposed to certain ultraviolet light. Typically, they are used to monitor the activity of altered genes.
The lamb belonged to Inra's animal research unit, UECA, which sells its unmodified animals to a local abattoir but has no right to sell GM animals.
An internal investigation into the huge slip-up suggests foul play on the part of an employee acting out of revenge after a dispute with a colleague.
While Rubis was a class 1 GMO, in other words containing a gene posing "no or negligible risk" to humans, Gerard Pascal, a former Inra biochemist, told Le Parisien its introduction into the human food chain was "intolerable".
"Beyond the ethical issues, one cannot put foodstuffs into the market that haven't been the subject of deep research," he said.
Placing on the market a genetically modified product or containing such organisms carries a maximum year's prison sentence and 75,000 fine.