Research question: Professional sports fulfil important societal functions. Previous studies have already attempted to quantify the intangible benefits of successful national athletes or hosting major sporting events. This study chooses an alternative channel of quantification. Based on the theoretical framework of sporting role models, it analyses whether the individual relevance of professional sports increases the frequency of sport participation. To quantify this effect, it subsequently analyses whether the increased sport participation increases sport-related expenditure.Research methods: A quantitative research design based on primary data of approximately 500 German amateur tennis players was chosen. Unfortunately, the econometric identification of the effect of the relevance of professional sports on sport participation behaviours is aggravated by a selection bias. To circumvent this issue, instrumental variables were constructed based on the starting year of the surveyed amateurs' sport participation, which is considered to be exogenous. Results and findings: The results of the instrumental variable estimations show that amateurs with a higher relevance of professional tennis spend between 21.5% and 24.4% more time playing tennis. In addition, 1% more participation per week increases the yearly sport-related expenditure by approximately 0.45%. Consequently, approximately 200 million euros of the tennis-related expenditure of German amateur tennis participants could be attributed to professional tennis in Germany. Implications: The results of this study provide evidence for positive external effects of professional sports in Germany. These external effects could act as an additional rationale for the use of public funds to promote professional sports.