The company said the object was discovered at an outlet in the northern city of Misawa, in a nugget sourced from a Thai company it had switched to in the wake of a food scare at one of its Chinese suppliers.
In July, Chinese officials shut food supplier Shanghai Husi Food Co following a television report alleging the plant mixed out of date meat with fresh product that was then supplied to McDonald’s and other major fast food chains.
The crisis prompted the Japanese arm of the global firm to drop Chinese poultry suppliers and switched to manufacturers in Thailand.
The latest incident drew widespread media attention on Monday with the story covered by Japan’s national broadcaster NHK and the top selling Yomiuri newspaper.
It comes less than two weeks after the Japanese unit said an emergency airlift eased a french fries shortage which forced the chain to ration the popular treat at more than 3000 restaurants across the country.