Place the chicken, celery, blue cheese, red onion, buffalo sauce, garlic, breadcrumbs, and egg in a bowl. Wet the slices of bread, squeeze the excess water out, and add them to the bowl.
You are going to need to brown the meatballs in three batches. Pour a tablespoon of olive oil into a skillet and heat over medium. I like to form the meatballs and add them directly to the skillet.