The reliability of realistic M3Y effective NN interactions to describe multistep direct (MSD) processes is proved by analyzing the corresponding real optical potentials. This trial is done in order to overcome the uncertainties of the effective NN-interaction strength V 0 obtained by direct fit to the experimental data. The microscopic potential for the nucleon–nucleus scattering at energies lower than 50 MeV has been calculated by using nucleonic and mesonic form factors. It has been analyzed through (i) a comparison with phenomenological optical potentials, and (ii) its use for description of nucleon elastic-scattering angular distributions. It results that the strongly simplified model interactions usually involved within MSD reaction theory, e.g. 1 fm range Yukawa (1Y) term, neglect important dynamical details of such processes. An 1Y-equivalent V 0 strength of a realistic effective NN interaction is determined by corresponding optical-potential volume integrals, and involved within Feshbach–Kerman–Koonin theory calculations.