I have a 4.75 boneless Butterball turkey breast in my frig. This is what the package says (word for word) about cooking it in the crock pot:
Crock pot
Roast must be thawed
1) Place thawed roast, skin side up, flat in 8 inch diameter crock pot
2) Add 1/2 cup water
3) Cover, cook on low 7 1/2 hours* to internal temperature of 170 in center
4) After 4 hours, check temperature at center, ends and near top for food safety. Turkey must reach 140 within 4 hours.
*Cooking up to 9 hours does not impair eating quality. (Cooking on high for the first hour does not reduce cooking time).
Hope that helps!