The magnetoresistance of a two-dimensional electron gas (2DEG) subjected to a weak two- dimensional (2D) lateral superlattice potential is expected to reflect the peculiar self-similar energy spectrum of Bloch electrons in a magnetic field, i.e., the splitting of Landau levels (LLs) into sublevels. One experimentally established effect of a periodic potential is that the discrete LLs are transformed into Landau bands and cause magnetoresistance oscillations due to an extra band- conductivity contribution. Theoretically, this band-conductivity contribution is expected to be suppressed if the splitting of the Landau bands is resolved. We study the suppression of the band-conductivity as a function of the electron mobility at millikelvin temperatures. Microfabricated gates, defined on top of high mobility GaAs/AlGaAs heterojunctions. are used to electrostatically impose a 2D-periodic potential with 150 nm period upon the 2DEG. By applying a positive bias the electron mobility is increased and we find the band- conductivity effectively suppressed if the mobility is well above 1 × 106 cm2/Vs.