Previously, we have proposed a relationship between the adsorption modes of a simple molecule (NO) and the behavior of the nanometer-scale monometallic clusters after this adsorption. More precisely, a set of experiments seems to show that dissociative adsorption of NO leads to the sintering of nanometer-scale metallic particles (NSMPs), whereas molecular adsorption is related to the oxidation. Although numerous investigations have been published on catalytic or electrocatalytic reactions where the interaction between carbon monoxide and NSMPs is involved, only a few studies have been dedicated to the adsorption of CO on NSMPs. This purely energetic approach is discussed through different results already published in the literature and through some recent theoretical calculations related to solid state physics. Although interesting and systematic results are gathered here and are partly explained, this adsorption process still remains a challenge.