  We investigate the influence of the allowed unphysical meson decay into a
quark-antiquark pair of the three flavour Nambu--Jona-Lasinio (NJL) model on
its parameter fixing. This decay manifests in a non-vanishing imaginary part of
the corresponding meson propagator and its polarisation loop, respectively. In
order to handle the emerging divergent integrals, we focus on the
Pauli-Villars, three- and four momentum cutoff regularisation method. Here, we
fix the parameters to certain observables, which are effected by the
non-vanishing imaginary part. The resulting parameter-sets for each
regularisation scheme are compared to each other with and without taking the
imaginary part of the polarisation loop into account.
