Theory is presented for the phase stability of mixtures containing nanospheres and non-adsorbing reversible supramolecular polymers. This was made possible by incorporating the depletion thickness and osmotic pressure of reversible supramolecular polymer chains into generalized free-volume theory, recently developed for investigating the phase behaviour of colloidal spheres mixed with interacting polymers (Fleer and Tuinier 2008 Adv. Colloid Interface Sci. 143 1-47). It follows that the fluid-fluid phase stability region where reversible supramolecular polymer chains can be mixed with nanospheres is sensitive to the energy of scission between the monomers and to the nanoparticle radius. One can then expect the fluid-fluid coexistence curves to have a strong dependence on temperature and that shifting of phase boundaries within a single experimental system should be possible by varying the temperature. The calculations reveal the width of the stability region to be rather small. This implies that phase homogeneity of product formulations containing reversible supramolecular polymers is only possible at low nanoparticle concentrations.