It was recently reported that segregation of Zr to grain boundaries (GB) in nanocrystalline Cu can lead to the development of disorder in the intergranular structure [1,2]. In this study we employ atomistic computer simulations to investigate how this disorder affects dislocation nucleation from the GBs under applied stress. It was found that a fully disordered grain boundary structure suppresses dislocation emission and significantly increases the yield stress. Depending on the solute concentration and heat-treatment, however, partial disorder may also occur and this aids dislocation nucleation rather than suppressing it, reducing or eliminating the strengthening effect.