Introduction: Only about half of the patients treated with Cognitive Behavioural Therapy (CBT) for depression are in remission after treatment. Progress monitoring during therapy, supplemented with clinical support tools, has shown promising results with regard to improving outcome, but results for group psychotherapy are less favourable. Therefore, we propose supplementary individual therapy as a possible solution to lack of progress in group CBT. The current study seeks to develop a brief add-on course of personalized individual therapy for patients showing lack of improvement during CBT group therapy. Methods and analysis: We aim to develop an intervention that includes progress monitoring, clinical support tools and a selection of patient-centred add-on interventions. An initial multiple case study will involve patients treated for depression in group CBT. The patients will perform progress monitoring every week, and therapists will receive alerts when a patient is not improving. Analyses will integrate qualitative data on the experiences of therapists and patients, quantitative tracking data, and initial clinical assessments. Based on these analyses, the proposed add-on interventions will be further developed and offered to the patients who are persistently not improving (pNOT) in three new CBT groups, which will be monitored as described above. Interviews will be performed with patients and therapists to explore their experiences of the new interventions. Qualitative data will be analysed through thematic analysis, and Single Case Experimental Design analyses will be made based on daily tracking of WHO-5.