How to make my new puppy stop stressing out my Dog?

The puppy is a full Breed GSD and he keeps chasing and stressing out my Cocker Spaniel. Now whenever the puppy comes close to him, he growls and i am afraid that a fight might break out. The puppy always tries to playfully bite him, but he finds that very annoying. WHAT CAN I DO? I dont want any one of them to get hurt. HELP PLEASE