A man gets turned into a dog like creature on an alien planet

Hi everyone. I'm trying to recall the name of a book I read in junior high, so around 1995-96. As I remember it a man ended up on another planet or in another world, and awoke in a cage. His captor was a woman, some kind of witch or sorceress, and as punishment for him being rude to her she transformed him into this long-legged dog-like creature (imagine a maned wolf for what I mean). He has to travel as the dog to complete some kind of quest in order to be turned back into a human. The cover included images of the dog creatures and I remember they creeped me out because the legs were way too long in proportion to the body. Any help is most appreciated!