At present, rehabilitation robotics field has stressed on developing systems for enhancing the rehabilitation cycle, considering primarily the intervention stage of the process. However, the assessment of functional problems is essential to define optimal rehabilitation treatments. This paper presents a robot-based strategy for the evaluation of a disabling motor problem like spasticity. Focusing on the upper extremity, we use a collaborative robot for the limb mobilisation and, in this way, evaluate the resistance to move that is related to the spasticity level. As a result, an objective rating of spasticity is obtained.