The large-distance behavior of the Feynman propagator is investigated in a simple non-Abelian model of fermions and massless bosons that generalizes the model considered by Popov and Wu with isospin to the case of an arbitrary compact semisimple Lie group and space dimension d≤4. The leading infrared approximation for the asymptotic behavior is obtained by means of the renormalization-group method applied to the effective one-dimensional massless model that describes the eikonal approximation to the original field theory.