  In a recent paper, Nagaev cited the unpublished paper by Franck et al.to
support his theoretical model for the mechanism of the giant isotope effect
observed in La_{1-x}Ca_{x}MnO_{3+y} (x = 0.20, y > 0). His model suggests that
the off-stoichiometric oxygen content depends strongly on the oxygen isotope
mass, which leads to a giant oxygen-isotope effect. Here I show that his
theoretical model is not consistent with any experimental results (even the
results recently published by Franck et al.), and his estimate of polaronic
bandwidth is wrong due to his misuse of polaronic theories.
