Molecular dynamics simulations investigating the mechanical properties of nanocrystalline Al have revealed the importance of both dislocation nucleation at grain boundaries and subsequent propagation as possible rate-limiting microscopic plastic process. Here, we present an approach to determine the athermal stress-strain behaviour of selected dislocations as they propagate within the nanocrystalline environment. In the first case study, the critical resolved shear stress to depin resulting into a planar propagation is found to be 735 MPa. In a second case study, a pinned dislocation is found to cross-slip at a critical resolved shear stress of 372 MPa to circumvent a near unfavoured grain boundary region.