PurposeProfessional football clubs have increasingly initiated two corporate diversification strategies to enfold growth opportunities besides traditional income sources: business diversification and international diversification. Empirical findings from management and sport management literature provide inconclusive evidence on these strategies' financial performance effects, necessitating further research. The purpose of this article is therefore to investigate how both corporate diversification strategies affect the financial performance of professional football clubs.Design/methodology/approachA 15-year panel data set of English Premier League (EPL) clubs is examined, many of which have employed corporate diversification strategies. Measures for related business diversification (RBD) and unrelated business diversification (UBD) as well as international diversification are established from management literature. Based on fixed effects regression models, their effects on clubs' revenues and profitability are then examined.FindingsU-shaped effects from RBD on revenues and profitability are found, but no effects from UBD. These findings empirically support the theoretically appealing superiority of RBD over UBD and, with increasing levels of RBD, over a focused strategy in management literature. With international diversification, an inverted U-shaped effect on revenues is identified.Research limitations/implicationsDespite focusing only on the EPL, these findings provide new evidence of non-linear financial performance effects from corporate diversification strategies adding to (sport) management literature and setting the stage for future research on these strategies in professional football.Practical implicationsThese findings have significant implications for club managers' strategic growth opportunities such as new business models or geographic markets.Originality/valueThis is the first study to empirically examine the financial effects of corporate diversification strategies in the football market context.