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Hello and thank you for using this site to help you. There are a couple of ailments that can cause what you are seeing, of course you will want to look for the simpler problems first such as something stuck between the pads or toes of the foot preventing him from putting down the foot.
More serious/clinical: If he seems really off balance , if there is any head tilt or the eyes have rapid movement , then you may be seeing Vestibular disease. This is usually due to an inner ear infection and resolves over a couple of weeks but the ear would need treatment.
This breed of dog is prone to inflammation of the tissue that cushions the discs that run along the spine and in the neck. This will show a problem with walking and sometimes show a drunken gait. For this, X rays or a myelogram may need to be taken in order to diagnose. Generally, anti inflammatory and pain meds are tried first to reduce inflammation, if those do not work then steroids may be tried and lastly there is surgery.
If you are seeing this in the rear leg then you may be looking at a problem with the knee cap where it goes in and out of the joint, or there is a tear in the ligament , both would have the dog not bearing weight on the leg. IF there is a ligament problem, in smaller dogs strict cage rest for a few months is suggested, but it can also end up in surgery.
Disc issues lower spine http://www.petplace.com/article/dogs/diseases-conditions-of-dogs/brain-spinal-cord-nerves/intervertebral-disc-disease-ivdd---thoracolumbar-area-in-dogs
Vestibular disease: You can also google on youtube a video of a dog with vestibular to compare it http://www.petplace.com/article/dogs/diseases-conditions-of-dogs/symptoms/head-tilt--in-dogs-vestibular-signs