Belonging to a group is a natural need for human beings. Being left out and rejected represents a negative event, which can cause discomfort and stress to the excluded person and other members. Social robots have been shown to have the potential to be optimal tools for studying influence in group interactions, providing valuable insights into how human group dynamics can be modeled, replicated, and leveraged. In this work, we aim to study the effect of being excluded by a social robot in a teenagers-robot interaction. We propose a conversational turn-taking game, inspired by the Cyberball paradigm and rooted in social exclusion mechanisms, to explore how the humanoid robot iCub can affect group dynamics by excluding one of the group members. Preliminary results show that the included player tries to re-engage with the one excluded by the robot. We interpret this dynamic as an included player's tentative to compensate for the exclusion and reestablish a balance, in line with findings in human-human interaction research. Furthermore, the paradigm we developed seems a suitable tool for researching social influence in different Human-Robot Interaction contexts.