Light incoherence due to quantum-gravitational fluctuations of the background space

Based on the theory of mutual coherence of light from an extended incoherent quasi-monochromatic source (providing a basis of stellar interferometry) we estimate the degree of light incoherence due to quantum-gravitational fluctuations of the background metric. It is shown that the stellar interferometry observational data considered in the literature for a last few years as a manifestation against the Planck scale quantum-gravitational fluctuations of the background metric have no chance for detecting such an effect.