Objective: Patient portals have the potential to support patient empowerment, self-care, and management, but their adoption and use have reported to be limited. Patients’ more active role creates tension, as health professionals need to change their traditional expert role and share control with patients. Professionals may also have other expectations and concerns that influence the acceptance of patient portals supporting patient empowerment. This study explores the health professionals’ expectations influencing their support for a new patient portal for self-management prior to implementation. Design: The study empirically evaluates the impact of several variables on health professionals’ support for a new patient portal for self-management. The study variables include 1) expected influences on professionals’ work, 2) expected influences on patients, 3) usability, 4) professional autonomy, 5) informing, 6) implementation practices, and 7) user participation. Methods: Data was collected through an online survey of 2943 health professionals working in 14 health organizations in Finland. The participating organizations run a joint Self-Care and Digital Value Services (ODA) project, developing a national patient portal for self-management. Three main services of the patient portal are well-being coaching, diagnostic tool, and a health care plan. Results and conclusions: The results show that health professionals’ positive expectations about the new patient portal, adequate informing of professionals ahead of time, and the organization's good implementation practices had a positive impact on their support for the patient portal. Perceived threat to professional autonomy had a negative impact on professionals’ support for the portal. Age, gender, and user participation did not influence support. Professionals’ concerns were related especially to patients’ willingness and capability to use the patient portal. The findings can guide health care providers to facilitate professionals’ support and remove obstacles to introduce patient portals already in the pre-implementation phase.