  In this paper we propose the study of the diffractive quarkonium
photoproduction in $pp$ collisions at LHC energies to probe the photon flux
associated to a ultrarelativistic proton. The total photon distribution is
expected to be given in terms of the elastic and inelastic components.
Distinctly from the elastic photon component which can be determined from the
elastic form factors, the magnitude of the inelastic component still is an open
question. We consider the current parametrizations for the photon distribution
of a proton and estimate the rapidity distributions and total cross sections
for the production of $J/\Psi$, $\Psi^{\prime}$ and $\Upsilon$ at LHC energies.
We demonstrate that the predictions associated to the inelastic contribution
are of the same order than those associated to the elastic one. Our results
implies that a dedicated experimental analysis of diffractive quarkonium
photoproduction with the tagging of the two protons in the final state can be
useful to constrain the magnitude of the inelastic component of the photon
distribution.
