Something on dog's leg

Can someone help me figure out what's on my dog's leg? He had dental work done about 10 days ago. He was licking the spot on his front leg where the iv was put in and I thought he was developing a bad hot spot so I took him back to the vet. He was given a steroid injection and he's been wearing an e-collar since then (5 days now). Now that he can't lick the area it's dried up and what's left is a yellow, hard spot that won't go away. Is it some sort of glue or dissolvable bandage that was left on after his iv was removed? It's peeling a little bit at one corner but is still very much attached to his leg, to the point that skin would come off if I pulled at it. I would assume if it's something that was supposed to dissolve it would have started to do so by now? Any help is appreciated!