In scale-invariant theories of gravity the Planck mass, which appears due to spontaneous symmetry breaking, can represent the only energy scale at the classical level. We discuss the possibility for the second scale, associated with the Higgs vacuum expectation value, to be generated by a quantum non-perturbative gravitational effect. The new scale can be orders of magnitude below the Planck scale, leading to the hierarchy between the electroweak and the gravitational forces. The effect is manifested in the existence of an instanton configuration contributing to the vacuum expectation value of the Higgs field. We study such configurations in several classes of theories motivated by phenomenology and identify conditions for the successful implementation of the mechanism.