Crookshanks, I think is part-kneazle, part cat. And I've never heard anything about kneazles being able to turn into humans.
But maybe it's not that much of a long-shot -- here's a link to a Mugglenet essay that speculates that Crookshanks may be the half-blood prince:
http://www.mugglenet.com/editorials/.../hope01.shtml. Crookshanks is described once or twice as being lion-like, as is the newly-descrbed character.
Here's my long-shot: The newly-described character, perhaps the new Defense Against the Dark Arts teacher, is somehow related to Godric Gryffindor -- much like Voldemort, the "heir of Slytherin," has snake eyes now, this new person (the "heir of Gryffindor"?), has some lion-like characteristics.
Maybe we're both right?