You should not wait to get it checked out. When things like this happen it could be something that is much more serious than a sprain. If the dog is limping on it then there is some pain there. If there is a tumor there it is best to catch it right away so that it can be addressed.
A sprain would be a good thing in this situation.
Please take the dog in to be checked out.
Let us know how you make out.
I completely agree with Red's assessment of the situation. Especially since there is some swelling there. If it turns out to be a minor sprain, great! But it's best to get it checked out now, because if there does turn out to be a mass involved, it can be removed early on to facilitate a speedy recovery or, heaven forbid, in the event it could be malignant, give the animal the best chance of being able to be cancer-free. I know I'm really jumping the gun here, but with a senior dog, which an eight year old shepherd definitely is, you can never be too careful.
Please let us know what happens.
Ghilly