The magnetic response of CeNi0.9Cu0.1 has been measured over a wide range of temperatures using both inelastic neutron scattering and detailed DC and AC magnetic susceptibility measurements. The purpose of these measurements was to clarify the role of Ce–Ni interactions in the formation of the CeNi intermediate-valence ground state. The results indicate that substitution of Ni by Cu results in a strong decrease of hybridization between the 4f and conduction band electron states, with the Ce ions changing character from an intermediate valence state in CeNi to a heavy-fermion short-range-correlated state in CeNi0.9Cu0.1.