  Within the framework of the $1/N_c$ expansion of four-fermion interaction
models, we analyse the next to leading $1/N_c$ corrections to the well known
large-$N_c$ result $M_S=2M_Q$ where $M_S$ is the mass of the scalar boson and
$M_Q$ is the constituent quark mass. The calculation is performed in the
Extended Nambu-Jona Lasinio (ENJL) model which is suitable for describing low
energy hadron properties. We treat the model as fully non renormalizable and
discuss the comparison with approaches based on the equivalence with
renormalizable Yukawa type models. We consider both the $G_V=0$ and the
$G_V\neq 0$ cases with $n_f=2$ flavours and study the dependence upon the
regularization scheme. We find that pure next-to-leading $1/N_c$ corrections
are large and negative, while a partially resummed treatment can induce
positive and smaller corrections. A triplet-singlet states' splitting is
observed.
