  We derive a redshift drift formula within the framework of varying speed of
light (VSL) theory using the specific ansatz for the variability of $c(t) = c_0
a^n(t)$. We show that negative values of the parameter $n$, which correspond to
diminishing value of the speed of light during the evolution of the universe,
effectively rescales dust matter to become little negative pressure matter, and
the cosmological constant to became phantom. Positive values of $n$ (growing
$c(t)$) make VSL model to become more like Cold Dark Matter (CDM) model.
Observationally, there is a distinction between the VSL model and the
$\Lambda$CDM model for the admissible values of the parameter $n \sim -
10^{-5}$, though it will be rather difficult to detect by planned extremely
large telescopes (E-ELT, TMT, GMT) within their accuracy.
