Here, we describe a highly sensitive method that allows for the correct quantification of inhibition effect with a higher degree of accuracy directly at the molecular level. The protocol involves two stages, namely serological virus titration in comparison with the same procedure for virus-effector mixture. Owing to the robustness of the analysis this assay can be performed on crude cellular and plant extracts, and therefore it may be suitable for the routine analysis of clinical samples, or in the field. The efficiency of the approach to the quantification of the inhibition effect of polysaccharide glucuronoxylomannan (GXM) on the infection efficiency of the tobacco mosaic virus (TMV) was investigated using advanced serological approaches based on label-free surface plasmon resonance technique. It was shown that GXM drastically decreases the efficiency of TMV infection by blocking up to 70% of the virus shell. The obtained results are in conformity with the method of indicator plant infection.