Suppose we have a hydrogen molecule $\ce{H2}.$ At room temperature the average distance of the nuclei is $r_0$ (without applying pressure).
If we put $n$ hydrogen molecules in a box with volume $V_\mathrm b < nr_0^3$ and the box isn't compressible, then the hydrogen atoms will be under pressure and will be forced to come closer than $r_0.$
Does that change the energy of the molecular orbitals, and if so, how?