It's possible he has panosteitis. Both of our guys had it. Very painful for them. Crate rest and walking just to potty really helped, plus they were put on a round of Rymadil (not sure if I spelled that right). Bassets are prone to get it, they are considered a large breed dog, usually around 8 months to 16 months of age, and males seem to be more prone than females. Taking him to the vet is a wise decision. I copied the rest off Vet Centric on the internet.
Panosteitis, eosinophilic panosteitis
Panosteitis, growing pains
AffectedAnimals:
Dogs.
Overview:
Rapidly growing dogs may experience pain that arises from the long bones in the limbs. These "growing pains" are known clinically as panosteitis, a disease affecting young dogs between the ages of five to 12 months. Lameness that shifts from leg to leg is a common symptom of panosteitis. Nausea and fever may occur as well. Although the pain associated with panosteitis can be acute, this discomfort -- along with the other symptoms -- almost always goes away once the dog has matured.
Large breeds, particularly the German shepherd, are most commonly affected by panosteitis, which also is reported fairly frequently in the golden and Labrador retriever, Great Dane, Scottish terrier, and Doberman pinscher breeds.
Clinical Signs:
Long bone pain, shifting leg lameness, fever, anorexia, lethargy.
Symptoms:
Lameness that may shift from limb to limb, pain, fever, and loss of appetite.
Description:
Affecting young, rapidly growing dogs of larger breeds, panosteitis is a disease that causes inflammation in the marrow cavities of long bones such as the humerus, radius, ulna, femur, and tibia. This inflammation leads to pain and the production of reactive bone that results in lameness and sometimes fever.
Sure hope he gets better quickly. Keep us posted.