We consider the effect of the uniaxial strain applied to a graphene monolayer with a realized quantum valley Hall state, for which we use a version of the Haldane model. In its specific point, the latter model has two spectral valleys: the gapless one and the gapped one. Using analytical and numerical arguments, we show that this state is unstable against mechanical deformations of the lattice, which influences the energy spectrum, the density of states, and the conductivity tensor.
