My dog is afraid of my new puppy. What should I do?

My five year old Bichon mix Lucky is afraid of our new Collie puppy Sadie who is eight weeks old. She is still a lot smaller than him, but he is absolutely terrified of her. Whenever she tries to play with him, He'll bare his teeth at her and go hide. I am really not sure what the problem is because he has been around other puppies before and Sadie is pretty submissive. Any suggestions of what I should do?