The number of physiotherapists and occupational therapists is not sufficient to cope with the demands of the increasing number of stroke survivors worldwide. These patients need specific training to promote recovery and prevent stroke-related disability. The paper discusses aspects how a social humanoid robots might serve as therapeutic assistant. It is not intended to replace human therapists, but to provide them with therapeutic assistance once therapeutic decisions are taken and the therapy has been introduced to the patient by the human therapists and the day to day practice needs to be supervised. The paper provides a case study of an HCD approach and exemplifies the strategy of digitalizing training tasks, the identification of exceptions, and ways of modelling the dynamic behaviour of the humanoid robot. This is demonstrated by task models. Some extensions of task models are suggested.