This article explores the following questions: (1) To what extent and in relation to which activities do football players perceive actions of their agents that are directed against their own interests depending on their performance levels? (2) Are players’ agents monitored by their players, and if so, in relation to which activities? (3) Which factors influence the monitoring behaviour of players? The relationship between the actors is modelled as a principal–agent relationship. The explorative study includes a dataset of 336 professional German football players. A logistic regression model was used to consider relevant factors influencing players’ monitoring behaviour. The results indicate that players’ agents across all leagues take actions potentially harmful to the players and show that approximately 50–60% of the players had their current agent monitored. Monitoring behaviour is influenced by ‘selection criteria’ and ‘framework conditions of the working relationship’, but not to the extent that could be expected. The research helps to understand the increasingly important relationship between players and agents. Players need to be aware that agents pursue their own objectives, which could be against the players interests. Therefore, monitoring is necessary. But data also show a lack of transparency, so that players do not know what agents are allowed to do and what is forbidden. If the associations and/or the players’ unions want to prevent possible damage to the players by their agents, it seems advisable to intensify and support information and awareness-raising campaigns or to adopt new statutes that regulate the players’ agents market more closely.