The present work applies the reduced statistical operator obtained by the derivation of a system-background model from non-equilibrium dynamics to the appearance of Rydberg atoms in an interacting environment with special attention to a plasma. The results are discussed particularly with regard to the effects of the coupling to the bath on the quantum states of the Rydberg atom. On the basis of a master equation we study the localisation of the bound electron, the transition to classical behaviour and the introduction of robust states as well as the validity of semi-classical approximations. Besides, it is shown, that the robust states of the heavier plasma component, the ions, allows a classical description, as for the lighter component, the electrons, a full quantum treatment is necessary.