  The interaction-induced orbital magnetic response of a nanoscale ring is
evaluated for a diffusive system which is a superconductor in the bulk. The
interplay of the renormalized Coulomb and Fr\"{o}hlich interactions is crucial.
The magnetic susceptibility which results from the fluctuations of the uniform
superconducting order parameter is diamagnetic (paramagnetic) when the
renormalized combined interaction is attractive (repulsive). Above the
transition temperature of the bulk the total magnetic susceptibility has
contributions from many wave-vector- and (Matsubara) frequency-dependent order
parameter fluctuations. Each of these contributions results from a different
renormalization of the relevant coupling energy, when one integrates out the
fermionic degrees of freedom. The total diamagnetic response of the large
superconductor may become paramagnetic when the system's size decreases.
