This contribution investigates whether a regulatory / enforcement gap exists in the current EU system of concentration control and if so, what is its degree of seriousness, in order to possibly warrant regulatory intervention at EU level. In this respect, the evidence stemming from economic theory regarding the potential anticompetitive effects that (non-controlling) minority stake acquisitions may give rise to, is discussed. Furthermore, the existing constraints (mainly related to company law instruments) that may alleviate the need for merger control intervention are dealt with. Also, the appropriateness of the existing legal tools is evaluated, with a reference to the Commission's past practice and the case-law of the EU Courts. In this respect, due attention is paid to the Ryanair / Aer Lingus case, given the complex problems it raised in connection with non-controlling minority shareholding acquisitions. This contribution concludes that the European merger control system exhibits certain enforcement / regulatory gaps that may indeed require (regulatory) intervention.