  We perform an analysis of triangle- and box-loop contributions to the
generalized potential in the scattering of Goldstone bosons off the J^P= 0^-
and 1^- charmed mesons. Particular emphasis is put on the use of on-shell mass
parameters in such contributions in terms of a renormalization scheme that
ensures the absence of power-counting violating terms. This is achieved with a
systematically extended set of Passarino--Veltman basis functions, that leads
to manifest power-counting conserving one-loop expressions and avoids the
occurrence of superficial kinematical singularities. Compact expressions to
chiral order three and four are presented that are particularly useful in
coding such coupled-channel systems. Our formal results are generic and prepare
analogous computations for other systems, like meson-baryon scattering from the
chiral Lagrangian.
