  We investigate the point-particle limit of the equations of motion valid for
a system of extended bodies in a scalar alternative theory of gravitation: the
size of one of the bodies being a small parameter xi, we calculate the limit,
as xi tends towards 0, of the post-Newtonian (PN) acceleration of this small
body. We use the asymptotic scheme of PN approximation, that expands all
fields. We find that the PN acceleration A of the small body keeps a
structure-dependent part at this limit. In particular, if the only massive body
is static and spherical, then A differs from the PN acceleration of a test
particle in a Schwarzschild field only by this structure-dependent part. The
presence of the latter is due to the fact that the PN metric depends on the
first spatial derivatives of the Newtonian potential. Since just the same form
of PN metric is valid for the standard form of Schwarzschild's solution, the
acceleration of a small body might keep a structure-dependent part at the point
limit in general relativity also, depending on the gauge. The magnitude of the
structure-dependent acceleration is already challenging on Earth. For the
Pioneer spacecrafts, it is likely to discard the current version of the scalar
theory. A modified version has been outlined in a quoted reference.
  Keywords: Weak equivalence principle violation, Asymptotic post-Newtonian
scheme
