  The effect of spontaneous breaking of chiral symmetry over the spectrum of
highly excited hadrons is addressed in the framework of a microscopic chiral
potential quark model (Generalised Nambu-Jona-Lasinio model) with a vectorial
instantaneous quark kernel of a generic form. A heavy-light quark-antiquark
bound system is considered, as an example, and the Lorentz nature of the
effective light-quark potential is identified to be a pure Lorentz-scalar, for
low-lying states in the spectrum, and to become a pure spatial Lorentz vector,
for highly excited states. Consequently, the splitting between the partners in
chiral doublets is demonstrated to decrease fast in the upper part of the
spectrum so that neighboring states of an opposite parity become almost
degenerate. A detailed microscopic picture of such a "chiral symmetry
restoration" in the spectrum of highly excited hadrons is drawn and the
corresponding scale of restoration is estimated.
