  We report on the pressure effects on the orbital polaron lattice in the
lightly doped manganites $\mathrm{La_{1-x}Sr_xMnO_{3}}$, with $x\sim 1/8$. The
dependence of the orbital polaron lattice on $negative$ chemical pressure is
studied by substituting Pr for La in
$\mathrm{(La_{1-y}Pr_y)_{7/8}Sr_{1/8}MnO_{3}}$. In addition, we have studied
its hydrostatic pressure dependence in
$\mathrm{(La_{0.9}Pr_{0.1})_{7/8}Sr_{1/8}MnO_{3}}$. Our results strongly
indicate that the hopping $t$ significantly contributes to the stabilization of
the orbital polaron lattice and that the orbital polarons are ferromagnetic
objects which get stabilized by local double exchange processes. The analysis
of short range orbital correlations and the verification of the Grueneisen
scaling by hard x-ray, specific heat and thermal expansion data reinforces our
conclusions.
