Starting from the Frank-Oseen free energy, the elastic forces of a thin nematic liquid-crystalline film between a cylinder and a planar substrate are calculated. The boundary conditions are assumed to be homeotropic. The repulsive forces obtained are found to be too small to be responsible for the elastic background frequently measured in surface forces apparatus experiments. Results from grand-canonical-ensemble Monte Carlo simulations which do not take into consideration a global deformation of the director field are sufficient for describing the experimental data. Repulsive forces appear to be a consequence of reorientations within intermediate strata between the fully developed molecular layers in the microscopic structure of the liquid-crystalline film.