In this work a comprehensive framework for modelling solvent-polymer mutual diffusion coefficient in the glassy state is proposed. This framework is based on irreversible thermodynamics. In particular, an appropriate transformation is used to show that case-II diffusion appearing in the glassy state could be reduced to a close-to-equilibrium rubbery state where typical equations relating the solvent-polymer mutual diffusion coefficient with chemical potential and the solvent self-diffusion coefficient are available. Moreover, this theory is applied to solvent evaporation from a toluene-poly(methyl methacrylate) film. The toluene evaporation process is modelled as a coupled heat and mass problem with a moving boundary. Model predictions were found to be in satisfactory agreement with available experimental data. It is believed that this work could be used to further study solvent diffusion in the glassy polymer state.