Sprinkle salt and pepper all over the inside of the chicken. Put the whole apple inside the chicken cavity and place chicken into a slow cooker, breast-side down. Pour apple juice around chicken.
Cook on Low until chicken is no longer pink at the bone and the juices run clear, 4 to 6 hours. An instant-read thermometer inserted into the thickest part of the thigh, near the bone, should read 165 degrees F (74 degrees C). Remove from the slow cooker, cover with a doubled sheet of aluminum foil, and allow to rest in a warm area for 10 minutes before slicing.