  We derive the 1-loop effective action of the cubic Galileon coupled to
quantum-gravitational fluctuations in a background and gauge-independent
manner, employing the covariant framework of DeWitt and Vilkovisky. Although
the bare action respects shift symmetry, the coupling to gravity induces an
effective mass to the scalar, of the order of the cosmological constant, as a
direct result of the non-flat field-space metric, the latter ensuring the
field-reparametrization invariance of the formalism. Within a gauge-invariant
regularization scheme, we discover novel, gravitationally induced non-Galileon
higher-derivative interactions in the effective action. These terms, previously
unnoticed within standard, non-covariant frameworks, are not Planck suppressed.
Unless tuned to be sub-dominant, their presence could have important
implications for the classical and quantum phenomenology of the theory.
