This can be due to ear infection. Floppy ears dogs have more problems then the erect ear dogs. Flaps which cover the ear canal, creating a warmer, darker environment where germs and other unwanted visitors can grow and flourish. Take your pet to the vet follow the vet advise. Once it is healed up and every thing is fine. Kindly check your dog regularly if you find dirt with in it or foul smell use ear cleaner to clean the ear. Put cotton in ears while giving bath to your dog this will prevent your dog chances of getting infection.