Blended learning has been increasingly implemented in higher education with the desire to transform teaching and learning. However, little of extant literature focuses on the perspectives of teachers who are the crucial change agents in the adoption of blended learning. This mixed-methods study utilized the Concerns-Based Adoption Model (Hall, 1973) to investigate how teachers were concerned about the top-down decision to adopt blended learning in a Vietnamese university. The Stages of Concerns Questionnaire was administered to 165 academic staff to explore their concern profiles, and follow-up semi-structured interviews were then conducted with 16 teachers to delve into their specific worries. The findings showed that the teachers’ concerns were most intense in the informational, awareness, and personal stages respectively, and lowest at the consequence and collaboration levels. Specifically, the teachers defining themselves as non-users or novices of blended learning were anxious about the compatibility of the approach to the local context where the teachers still had limited knowledge and skills required for blended learning implementation. These findings not only inform policymakers of the teachers’ apprehension and voices but also raise significant implications for providing teachers with sufficient professional development to ensure the successful promotion of blended learning at the institution.