  Pionium lifetime corrections to the nonrelativistic formula are calculated in
the framework of the quasipotential-constraint theory approach. The calculation
extends an earlier evaluation, made in the scheme of standard chiral
perturbation theory, to the scheme of generalized chiral perturbation theory,
in which the quark condensate is left as a free parameter. The pionium lifetime
is calculated as a function of the combination $(a_0^0-a_0^2)$ of the $\pi\pi$
S-wave scattering lengths with isospin I=0,2.
