Campbell went to the HemoRio medical center on Tuesday to take part in a blood drive, but was turned away. Officials there say she needs to wait longer after having surgery in February to remove a cyst.
An outbreak of mosquito-borne dengue fever has infected more than 75,000 people in Rio de Janeiro state this year and killed at least 80.
Campbell often visits Brazil and Rio Mayor Cesar Maia has invited her to be a goodwill ambassador for the city.
