Complete and Sudden Change in Dog's Behavior

S.:

That soft knot is most likely cancer or fatty globule which is resting or sitting on the nerve and muscle of the leg.

It could be an infection - it could be the dog was bit by something (tick, snake) when outside and now its infected.

The vet will most likely shave the area where the lump is to see it better. They may try to aspirate it to see WHAT it is. The vet will most likely do X-Rays as well to determine if something is broken or if it is cancer - how much it has spread, where it is. that's worst case scenario. best case? tick or some type of bite that is infected!

Good luck!

It was bone cancer for our dog. She went fast. Hope it's something fixable.

Sounds like what happened to my BIL's dog - it was cancer and they put him down :(
Is he still eating?

It could be a torn ACL. My dog suffered that once, and acted just like this and had the same symptoms. She needs to take her to the Vet asap. There is a surgery that can be done to repair it if it's the ACL. Praying that is what it is and not what the other posters have said about cancer! :(

My dog had something similar this past fall- he's 12 years old. We thought he was nearing the end. He was limping, acting lethargic, had a knot on his leg, and just generally not his normal peppy self. I was preparing myself for the worst.
Well, turns out it he tested positive for an uncommon tick born illness. We never saw the tick and were religiously giving him flea/tick medication! He had probably had the illness for a while, but the symptoms just came on suddenly one day.
After a round of antibiotics, he was back to normal.
You just never know. Don't assume the worst until you know for sure.

so glad she has made an appointment with the vet. My SIL's dog had a lump on her leg. She waited, hoping it would go away or something. Of course it didn't. It got so big that the dog could hardly walk, so they finally took her in. It was not cancer but it was an infection and the poor dog had to have its leg removed. Cancer or not, its good to find out sooner rather than later. My sisters pug got cancer and is now in remission. Good luck to your friend.

Could be as simple as a leg injury - pain may be making it difficult to get up to potty... could be something far more serious, like cancer :( hope the dog is better soon.

Ditto mamaduck (more or less). Our dog is older (8 1/2) and she began limping, getting slower, depressed, etc. I even took her to the vet assuming arthritis and the limp maybe being associated with landing funny from jumping for her frisbee (which she was doing less and less)...
They couldn't find anything specifically wrong, age related arthritis starting to set in is what they decided... but they didn't do any bloodwork.

A few months later, took her in for her annual exam, ran bloodwork, and found ehrlichiosis (tick borne disease that CAN cause serious problems including bleeding, but also can present subclinically and appear as achey joints, depression, lethargy). 24 hours on antibiotics and she hasn't had any arthritis symptoms since, even though it has been winter! She's like a puppy playing again.

I would not conclude ANYthing, until the vet has run blood work. And if they do not, I would specifically ask them to run tests for tick borne illness (and not just lyme--there are several others).

Hoping for a good outcome for your friend's furry companion.

So sad...maybe lime disease?