We present a direct study on the positioning and mobility of tetracene molecules in self-assembled methionine nanogratings on the Ag(111) surface. Our scanning tunneling microscopy observations reveal the preferential arrangement of isolated tetracene units within substrate stripes framed by one-dimensional methionine supramolecular rows, under the influence of long-range indirect interactions. However, the orientational order of the rod-like tetracene species is induced by the epitaxial fit to the underlying surface atomic lattice; and preferential alignment with the tetracene axes along the direction of the methionine grating could not be achieved. In scanning tunneling microscopy measurements under perturbative conditions, we find a one-dimensional diffusion of the confined tetracene along the direction of the molecular axis and restricted by the methionine gratings for non-parallel orientations.