This paper shows how a strain based hemolysis indicator can be built from a non-linear viscoelastic model describing the rheology of blood. It is shown that the principal stretches arising from the spectrum of a left Cauchy-Green elastic stretch tensor of the fluid can be used to estimate the areal strain (relative change of a fluid parcel surface area) under the flow conditions. The high areal strain can be used as an indicator of regions where stress induced hemolysis is occurring. This approach is put in the context of a similar model based on a fluid droplet analogy. Some first numerical simulations are presented for a case of smooth axisymmetric stenosis, pointing out the critical flow regions predicted by both approaches.