  We discuss the virtual Compton scattering amplitude $\gamma^\ast+\pi\to
\gamma+\pi$ which enters the reaction $\pi^-+e^-\to\pi^-+e^-+\gamma$. The
low-energy scattering amplitude is divided into a model-independent part,
involving only the electromagnetic form factor, and a residual part which
contains structure information related specifically to (virtual) Compton
scattering. In the limit of vanishing final-photon energy, the residual
amplitude can be expressed in terms of three generalized dipole
polarizabilities which are functions of the squared virtual-photon
four-momentum. We study the VCS amplitude in the framework of chiral
perturbation theory at ${\cal O}(p^4)$. At the one-loop level the generalized
dipole polarizabilities are degenerate
$\alpha_L(q^2)=\alpha_T(q^2)=-\beta(q^2)$.
