Microcracks in thermal barrier coatings are inherent from the plasma spraying process. Such cracks might constitute a threat to the coating. The influence of pre-existing cracks in the global direction of the interface between the bond coat and the top coat on the risk of delamination is addressed through finite element simulations. Stress concentrations at the interface due to the roughness of the plasma sprayed bond coat are accounted for by a sinusoidal interface. The effect of oxidation of the bond coat is modelled by including a thin oxide layer between the ceramic coat and the bond coat. It was found that the crack tip position of pre-existing cracks, as well as the presence of an oxide layer, significantly influences the risk of delamination. As the oxide thickness increases, the risk of crack propagation increases. It is also found that not all pre-existing cracks can propagate. For some crack tip locations, the crack remains closed during the entire loading sequence.