Evolutionary rescue is a process by which a population, having become prone to extinction due to environmental changes, recovers by evolutionarily adapting to the new environment. Genetic materials for adaptation may come from mutation, standing genetic variation, and hybridization with closely-related species. Although hybridization might potentially serve as a useful means to invoke evolutionary rescue for conserving threatened species, theoretical research has been limited. An exceptional pioneering model by Baskett and Gomulkiewicz explored theoretical conditions about when introgressive hybridization with a related viable species could rescue a focal species maladaptive to the novel environment. This model, however, only considers limited situations, where (1) an environmental change occurs instantly between successive generations, and (2) one of hybridizing species already possess alleles adaptive to the novel environment. By relaxing these assumptions, our model found that (1) evolutionary rescue is more likely with gradual environmental changes, and (2) transgressive segregation could lead to successful evolutionary rescue even if neither parental species had already adapted to the new environment. Our results may expand theoretical feasibility of evolutionary rescue by hybridization, but more theoretical research would be necessary for applying hybridization as a useful means to conserve threatened species in real cases.