  We calculate fermion-loop corrections to high energy $W^+W^-$ scattering in
the context of a Strongly Interacting Electroweak Symmetry Breaking Sector
(EWSBS) using Higgs Effective Field Theory(HEFT). We test the assumption that
these corrections are negligible when compared to the boson-loop ones, as it is
commonly taken for granted in the literature. While this is correct inmost
cases, we find that, for some particular regions of the parameter space,
fermion-loops can be important: deviations in the couplings of the HEFT from
their Standard Model values may lead to fermion-loop corrections as relevant as
the boson-loop ones.
