Single gold-carbonyl species adsorbed on a FeO thin film on Pt(111) exhibit a pronounced zero-bias conductance anomaly in scanning tunneling spectroscopy, while bare Au atoms reveal a smooth conductance behavior. The phenomenon is attributed to the Kondo effect, which seems to be triggered by AuCO attachment to the oxide surface but originates in fact from the interplay between the Fe magnetic moments and the Pt conduction electrons. This interpretation is supported by the observation of a similar conductance anomaly even for the pristine oxide film under certain circumstances. Apparently, the FeO/Pt(111) system is intrinsically susceptible to a Kondo-type behavior, which needs however to be initiated by a small, e.g., adsorbate-induced modification of its magnetic structure. The role of the AuCO in triggering the effect is explored by analyzing the geometric and electronic properties of the ad-complex on the FeO thin film via tunneling spectroscopy and density-functional theory.