1. Combine first 3 ingredients in a small bowl; set aside.
2. Place chicken in a medium bowl; add panko, carrot, celery, paprika, egg, and garlic. Mix just until combined. Divide into 8 portions; shape each into a 3-inch patty.
3. Heat a grill pan over medium-high heat. Lightly coat pan with cooking spray. Add patties to pan; cook 3 minutes on each side or until done. Combine hot sauce and butter in a medium bowl; add patties to bowl, turning to coat. Layer bottom half of each bun with 1 patty, about 1 teaspoon blue cheese mixture, 2 celery leaves, and top half of bun.