Multi-phase fluid conditions encountered in geotechnical and geo-environmental problems have led to the development of models that account for the influence of gas solubility and compressibility on the behaviour of soils of various grain sizes. Yet, no consideration has been given to damages related to the nucleation and growth of gas bubbles in fine-grained soils. The purpose of this paper is to present a Cam Clay based constitutive model extended to incorporate such detrimental effects on gassy soils. This is achieved by deriving an analytical expression relating the preconsolidation pressure to a damage parameter dependent on the gas content. That expression is coupled to a deviatoric yield surface accounting for inherent and stress-induced anisotropy. Comparisons of simulations and experimental results attest that introducing a single additional parameter to a conventional Cam Clay type model allows key behavioural features of gas-charged fine sediments to be reproduced.