  We investigate if the projected high-precision measurements of the cross
section of the Higgsstrahlung process $e^+ e^- \to Zh$ at a future
electron-positron collider can be utilised to indirectly probe the fermionic
Seesaw models. We consider the two centre-of-mass energies $\sqrt{s}=240$ GeV
and $365$ GeV, and compare the collider reaches to constraints from electroweak
observables, probes of lepton flavour universality and the existing and
prospective bounds from searches for lepton flavour violation. For the analysis
we assume the limit of an exactly conserved lepton-number symmetry. We find
that while any appreciable correction to the Higgsstrahlung cross section is
already strictly constrained in the Type-I Seesaw model, effects of up to
$\mathcal{O}(10\%)$ are possible within Type-III Seesaw.
