The surface tension, the adsorption, and the depletion thickness of polymers close to a single non-adsorbing colloidal sphere are computed by means of Monte Carlo simulations. We consider polymers under good-solvent conditions and in the thermal crossover region between the good solvent and θ behaviour. In the dilute regime, we consider a wide range of values of q, from q = 0 (planar surface) up to q ≈ 30–50, while in the semidilute regime, for ρp/ρp∗ ≤ 4 (ρp is the polymer concentration and ρp∗ is its value at overlap), we only consider q = 0, 0.5, 1 and 2. The results are compared with the available theoretical predictions, verifying the existing scaling arguments. Field-theoretical results, both in the dilute and in the semidilute regime, are in good agreement with the numerical estimates for polymers under good-solvent conditions.