In a medium saucepan over medium heat, slowly cook and stir skinless, boneless chicken breast halves, onion and garlic. Cook until onions are tender and chicken is lightly browned.

In a medium bowl, blend chicken mixture, cream cheese and butter until creamy.

Preheat oven to 325 degrees F (165 degrees C).

Unroll croissants and divide in half to create 12 rectangles. Place approximately one tablespoon of the chicken mixture on each rectangle. Fold into balls.

Arrange balls on a large baking sheet. Bake in the preheated oven 12 minutes, or until golden brown.