Context: Detailed rehabilitation protocols after stem cell treatment are lacking. This case highlights the rehabilitation of a patient treated with human umbilical cord blood-derived mesenchymal stem cell implantation for a large osteochondritis dissecans lesion of the knee. Case presentation: A 17-year-old male adolescent wrestler experienced persistent left knee pain for 1 year, unresponsive to 6 months of conservative treatment. MRI revealed a large osteochondritis dissecans lesion (38 × 18 mm) in the lateral femoral condyle, which was treated with human umbilical cord blood-derived mesenchymal stem cell implantation. Management and outcomes: Rehabilitation was conducted in 4 phases. The protection phase (1–8 wk) emphasized weight-bearing restrictions, continuous passive motion, and early gait training. The gait recovery phase (9–12 wk) incorporated stationary cycling and open kinetic chain exercises. During the maturation phase (13–24 wk), maximal strength and proprioception exercises were introduced with antigravity treadmill running. The final recovery phase (24–52 wk) focused on plyometric drills and sport-specific activities. Team training resumed at 32 weeks, and return to full competitive training occurred at 52 weeks. The limb symmetry index for isokinetic knee-extensor strength and single-leg hop test reached 95.2% and 97.9%, respectively, by 12 months, indicating near-complete functional recovery. The modified MRI of cartilage repair tissue score improved from 40 to 60 points between 1 and 3 years postsurgery. Second-look arthroscopy revealed an International Cartilage Repair Society grade 1 at 35 months. International Knee Documentation Committee scores increased from 17.2 preoperatively to 98.9 at 2 years, while visual analog scale scores decreased from 10 to 2 over 3 years. Conclusions: Accelerated weight bearing, early gait training, and phased strength exercises facilitated substantial improvements in function and cartilage healing in an adolescent wrestler with a large osteochondritis dissecans lesion. Further studies with larger cohorts are recommended to confirm these findings.