A new formulation for an elastohydrodynamic problem with degrading lubricant is proposed. The formulation takes into account stress-induced degradation of polymer additive to lubricant on the basis of the kinetic equation for polymer degradation. Degradation of polymer additive results in an irreversible viscosity loss, which, in turn, leads to a reduced lubrication film thickness and change in other contact parameters. The problem is solved numerically. A solution of the kinetics equation is compared with some experimental polymer degradation data. The calculated value of the viscosity loss in a lubricated contact is similar to an earlier obtained one in experiments.