Very difficult to see from the pic, but they could be scabs or infections either from an injury or moisture getting trapped against his foot. Do his branches stay moist or dry out completely. Pododermatitis (foot infection) can be challenging because if it progresses and goes into the deeper layers of the foot it can damage the bones and be very difficult to treat. If they were just spots I wouldn't be too worried, but since he doesn't want to use the foot much I'd have them checked by a vet in case treatment is needed.