Spray 5- to 6-quart slow cooker with cooking spray. Place chicken in slow cooker; top with butter. Pour cooking sauce over chicken.
Cover; cook on Low heat setting 4 to 6 hours or until chicken is very tender.
Using 2 forks, shred chicken in slow cooker. Add cream cheese. Cover; cook 30 minutes longer or until cheese is melted.
Meanwhile, cook and drain fettuccine as directed on package.
Stir chicken mixture; serve over fettuccine. Garnish with basil.