  We present a phenomenological study of the $x_F$ dependence of quarkonium
production in high energy proton-nucleus collisions. The \xf~dependence of
comover contributions is introduced to account for the observed quarkonium
suppression at low $x_F$. Combining comover contributions, nuclear shadowing
effect, energy loss mechanism and nuclear absorption together we reproduce the
overall \xf~dependence of E772/E789 data.
