  In composite Higgs (CH) models, large mixings between the top quark and the
new strongly interacting sector are required to generate its sizeable Yukawa
coupling. Precise measurements involving top as well as left-handed bottom
quarks therefore offer an interesting opportunity to probe such new physics
scenarios. We study the impact of third-generation-quark pair production at
future lepton colliders, translating prospective effective-field-theory
sensitivities into the CH parameter space. Our results show that one can probe
a significant fraction of the natural CH parameter space through the top
portal, especially at TeV centre-of-mass energies.
