  The $SU(3)$ chiral effective lagrangian at next-to-leading order is applied
to the S-wave meson-baryon interaction in the energy range around the $\eta N$
threshold. Potentials are derived from this lagrangian and used in a coupled
channel calculation of the $\pi N$, $\eta N$, $K \Lambda$, $K \Sigma$ system in
the isospin-$1/2$, $l=0$ partial wave. Using the same parameters as obtained
from a fit to the low energy $\overline{K} N$ data it is found that a
quasi-bound $K \Sigma$-state is formed, with properties remarkably similar to
the $S_{11}(1535)$ nucleon resonance. In particular, we find a large partial
decay width into $\eta N$ consistent with the empirical data.
