In this paper, we explore the signature of a simplified model which includes a new singlet scalar state and a vector like quark at future lepton colliders. In particular, we study the production of the new singlet scalar in association with a photon, which proceeds through loop level diagrams involving vector like top quark partner, at future e−e+ colliders with different center-of-mass energies from 500 GeV to 3 TeV. To show the sensitivity of the process, the exclusion limits on the parameter space of the model are presented considering the decay of the singlet scalar into a pair of Higgs boson, followed by the decay of Higgs bosons into b ̄b pairs. The results are compared to those obtained from the LHC, electroweak precision data and other channels at lepton colliders and it is shown that a notable sensitivity to the parameter space of the simplified model could be achieved
