My brocky has the same thing, only bigger and on his back leg. Its been there for ages, and the little guy is doing fine, full of life.
I rang this vet (I think his surname is greenwood) and he said that it sounded like a fluid filled abscess or something, not much to worry about, but to ring him back if it changed color or grew much bigger, or if it seemed to be hurting him or effecting his normal behaviour. Brocky, however, remains fine. Id say if your worried, check with a vet, but it looks like the same thing, only brock's is bigger. unless it changes your pet then just keep an eye on it.