  We investigate the nonlocal structure of optical model potentials for
nucleon-nucleus scattering based on microscopic approaches. To this purpose,
\emph{in-medium} folding optical potentials are calculated in momentum space
and their corresponding coordinate-space counterpart are examined, paying
special attention to their nonlocal shape. The nucleon-nucleon effective
interaction consists of the actual full off-shell $g$ matrix in
Brueckner-Hartree-Fock approximation. The nonlocality of effective interactions
is preserved throughout all stages in the the calculation. Argonne $v_{18}$
bare potential and chiral next-to-next-to-next-to-leading order bare
interaction are used as starting point. The study is focused on proton elastic
scattering off $^{40}$Ca at beam energies between 30 and 800 MeV. We find that
the gradual suppression of high-momentum contributions of the optical potential
results in quite different-looking coordinate-space counterparts. Despite this
non-uniqueness in their nonlocal structure, the implied scattering observables
remain unchanged for momentum cutoff above a critical one, which depends on
incident energy of the projectile. We find that coordinate-space potentials
with momentum cutoffs at the critical value yield the least structured nonlocal
behavior. Implications of these findings are discussed.
