[en] Green functions are used for incestigation of specific features of the nonlocal optical potential in the 0.1-6 MeV neutron scattering on a ⁹⁰Zr nucleus. The ''pure'' radial dependence for the imaginary part of the optical potential has been derived with allowance for its spherical symmetry. The energy dependences of the neutron optical absorption and scattering on ⁹⁰Zr cross sections are presented. On the basis of the spectral features of single-particle and collective excitations of the ⁹⁰Zr nucleus it is concluded that: 1) both the collective and noncollective mechanisms in a compound nucleus are important in the formation of the imaginary part of the neutron optical potential at the nonelastic scattering threshold energies, whereas the direct processes are inessential; 2) the contributions from the 2p-1h states to the imaginary part of the optical potential are associated with volume absorption, while contributions from the collective ''phonon-plus-particle'' states - with surface absorption; 3) the imaginary part of the optical potential and absorption cross section exhibit their dependence on the state density of a compound nucleus which agrees with the experimental behavior of scattering cross sections