Damage to a casing string in a wellbore resulting from a wellbore operation can be predicted. For example, a stiff string model can be used to determine a contact point between the casing string and a well tool positionable within the casing string for performing the wellbore operation. The stiff string model can be used to determine a force of the well tool against the casing string at the contact point. The force can be used to determine a volume of damage to the casing string proximate to the contact point. A depth of a groove formed in the casing string proximate to the contact point can be determined based on the volume of damage.