  In this paper we consider tree-level gauge invariant off-shell amplitudes
(Wilson line form factors) in $\mathcal{N}=4$ SYM with arbitrary number of
off-shell gluons or equivalently Wilson line operator insertions. We make a
conjecture for the Grassmannian integral representation for such objects and
verify our conjecture on several examples. It is remarkable that in our
formulation one can consider situation when on-shell particles are not present
at all, i.e. we have Grassmannian integral representation for purely off-shell
object. In addition we show that off-shell amplitude with arbitrary number of
off-shell gluons could be also obtained using quantum inverse scattering method
for auxiliary $\mathfrak{gl}(4|4)$ super spin chain.
