Hi,
It certainly sounds like there may be something structurall yabnormal about this leg, particularly if it has been like this from birth - does the dog put weight on it at all?
I would have him examined by the vet straight away to try to asess what the problem might be. If there is just a muscle sprain or strain then it may heal ok given rest,, but the vet may be able to manipulate a dislocation or abnormally developed area which may be much more of a cause for concern.
If this is the case then an xray may be necessary, which can usually be done in a small puppy pretty easily with just a little gas anaesthesia to keep him still. If there is damage to a leg it is important to identify it at a young age to make sure that everything possible can be done to help the function - bulldogs have quie a lot of body to carry artound on those legs and so need them to be as strong as possible. You also need to establish what effect this might have on your dog as he gets older too.
I hope this helps,
Jen
Dog Veterinarian
BVetMed MRCVS since 2004, have a high caseload of canine patients and perform acupuncture.
OK, I would definitely get it checked as it doesn't sound like it's much use to the dog at the moment,
Good Luck!