Temporal separation in diel activity between species can be caused either by different realized niches or by competition avoidance. Morphologically similar species tend to have similar ecological niches. Therefore, morphological similarities among sympatric species may be related to both overlap in diel activity and possibilities for competition. In carnivores, competition is often strong and asymmetric. Africa contains one of the most species rich carnivore assemblages in the world, where the African lion (Panthera leo) is dominant wherever it is present. Using camera trap data on South African carnivores, we evaluated how overlap with lions in diel activity related to similarities to lions in body mass, skull and long bone morphology. We found a positive association between overlap in diel activity with lions and similarities in log body mass, but we only observed this association using dry season activity data. We found no associations between overlap in diel activity with lions and similarities in either long bone or skull morphology, nor did we find associations between differences in overlap in diel activity within species between one reserve with and one without lions and morphological similarity with lions. Our results suggest that niche utilization rather than avoidance of lions dictated carnivore diel activity, although we acknowledge that lion avoidance could have been manifested in spatial rather than temporal separation. Our study supports recent suggestions of context dependencies in the effects of apex predator presences.