Keep tge dig seperate from your cat until he grows accustomed to the dog's presence.
That cat hides from him. He hated him yesterday. The cat stayed on top of my mom's computer tower and just sat there and growled while my older brother tried to "distract" him. Really my brother was seating him, staying him, and hitting him with his toys.
He's a shepherd dog, the dude is made for running, of course the cat is scared.