Botanical fungicides are an interesting alternative for pathogen control and plant protection in sustainable production systems. Thus, this study aimed to evaluate the potential of cinnamon for use in inhibiting pathogens in tomato crop. Three main strains of Fusarium oxysporum f. sp. lycopersici and a strain of Alternaria alternata were grown in in vitro conditions, and later used for tests of antifungal effect of cinnamon extract, compared to sodium hypochlorite. As a result, complete growth inhibition of the three strains of Fusarium oxysporum f. sp. lycopersici and Alternaria alternata were achieved only when using sodium hypochlorite from a concentration of 3%, and a partial inhibition with the use of cinnamon extract. Both, cinnamon extract and sodium hypochlorite solution, at concentrations above 2%, reduced Mycelial Growth Speed Index values. Cinnamon extract demonstrated its antifungal potential, indicating the possibility of its use in the in vitro control of phytopathogenic fungi in tomato crops. In addition, this study also showed the main effects of cinnamon extract on hyphae and conidia of these phytopathogens. [Correction added on 01 November 2022, after first online publication: The full form of 'MGRI' has been updated in the abstract of this version].