Felipe Kitadai said he was carrying the medal everywhere. He took it with him to the shower as a joke, then dropped it while trying to keep it from getting wet.
Kitadai told Brazil's GloboEsporte.com that the part holding the medal's string broke, and now he can't wear it around his neck. He said there's also a small dent on it.
Kitadai won the bronze in the men's 60-kilogram division Saturday.
The Brazilian Olympic Committee says it will request a new medal even though it knows the International Olympic Committee has no obligation to give Kitadai another one.