  Forward Drell-Yan production at high energy can provide important constraints
on gluon densities at small $x$, in the saturation regime. In this work we
focus on the nuclear modification of this process, which could be measured at
the LHC in the near future. For this we employ the color dipole approach, using
the optical Glauber model to relate the dipole cross section of a nucleus to
the one of a proton. Combining these results with our earlier results for
forward $J/\psi$ production, we compute the ratio of the nuclear modification
factors of these two processes. This observable was recently suggested as a way
to distinguish between initial and final state effects in forward particle
production.
