Little is known about the formation of expectations of return to work (RTW) from the perspective of injured workers with back injuries. This modified grounded theory study uses a biopsychosocial approach that considers the workers' complex social circumstances, to unpack the multidimensional construct of expectations of RTW from the injured worker's perspective. Initial semi-structured interviews were conducted with 18 individuals with sub-acute back pain, who were off work between 3 and 6 months. Follow-up interviews were conducted with 7 participants for the purposes of member checking. The interview data was coded, compared and analyzed over the course of data collection, until saturation was reached. Data analysis revealed that expectations of return-to-work are constructed based on perceived uncertainty which subsumes five inter-related categories (1) perceived lack of control over the return-to-work process, (2) perceived lack of recognition by others of the impact of the injury, (3) perceived inability to perform the pre-injury job, (4) fear of re-injury, and (5) perceived need for workplace accommodations. Expectations, once formed, were influenced by the worker's experience of coping with perceived uncertainty. Perceived uncertainty plays a key role in injured workers' formation of expectations of return-to-work. Implications are discussed regarding how this perceived uncertainty plays a role in the development of (re)injury prevention and rehabilitation programs. The importance of further research on perceived uncertainty is presented, along with potential future research considerations.