Infrared asymptotics of the Green's function of massive particles in a charge-symmetric model

The infrared asymptotic behavior is studied of a one-fermion Green's function in a model of a massive isospinor field interacting with a massless isovector. Approximate methods are suggested for computing the infrared asymptotic behavior both in the operator formalism as well as in the path integral method. The answers obtained coincide, although the approximations made when deriving them cannot be taken to be fully justified.