  We suggest a novel nonlinear $\sigma$-model for the description of disordered
superconductors. The main distinction from existing models lies in the fact
that the saddle point equation is solved non-perturbatively in the
superconducting pairing field. It allows one to use the model both in the
vicinity of the metal-superconductor transition and well below its critical
temperature with full account for the self-consistency conditions. We show that
the model reproduces a set of known results in different limiting cases, and
apply it for a self-consistent description of the proximity effect at the
superconductor-metal interface.
