Objectives: The aim of this prospective study was to examine the utility of an integrated model comprising constructs from self-determination theory (SDT) and the theory of planned behavior (TPB) in predicting adherence to a post-surgery rehabilitation program in patients receiving anterior cruciate ligament (ACL) reconstruction. Constructs of the integrated model measured at baseline were expected to predict patients' rehabilitation adherence two months later. Method: Patients (N = 121, M age = 27.62, range = 18–53; 36.66% female) scheduled to have ACL reconstruction surgery within two months were recruited from a Hong Kong public hospital. At baseline and two-month follow-up, patients completed measures of perceived autonomy support from doctors and physiotherapists and treatment motivation from SDT, social cognition constructs from the TPB factors, and adherence to the postsurgery rehabilitation program recommended by their surgeon. Results: Path analysis displayed good goodness-of-fit of the proposed model with the data (χ2 = 11.47 (df = 9), CFI = 0.98, TLI = 0.93, RMSEA = 0.06 [90% CI = 0.00; 0.10]) after controlling for age, gender, time of surgery, post-surgery rehabilitation, and injury severity. Consistent with hypotheses, perceived autonomy support from physiotherapist and autonomous treatment motivation directly and indirectly predicted the TPB constructs and treatment adherence. However, there was no association between perceived autonomy support from doctors and autonomous motivation. Conclusion: The integrated model was effective in explaining the psychological processes that relate to medical adherence. Findings also highlight the importance of the autonomy support from physiotherapists and provide evidence for potential intervention targets.