BACKGROUND: Assess the association between changes in injured leg knee extension and flexion strength (peak torque) and self-reported and performance-based measures of leg function after a variety of youth sport-related, time-loss knee injuries. HYPOTHESIS: There will be a relationship between changes in knee muscle strength and changes in measures of leg function in youth after a sport-related knee injury. STUDY DESIGN: Prospective cohort study. LEVEL OF EVIDENCE: Level 2. METHODS: This was a secondary analysis of the Alberta Youth Prevention of Early Osteoarthritis (PrEOA) Cohort study (Edmonton) that included youth (11-19 years old) who had experienced a medical attention, time-loss, sport-related knee injury in the previous 4 months. Injured leg knee extensor and flexor concentric peak torque (isokinetic; 90 deg/s), triple hop distance, modified Y-balance test (YBT), and Knee injury and Osteoarthritis Outcome Score Sport subscale (KOOS) were assessed at baseline (≤4 months postinjury) and 6 and 12 months later. Adjusted associations between 6- and 12-month change in strength and functional measures were assessed using multivariable regression (95% CI). RESULTS: Based on data from 106 participants (16.2 ± 1.8 years old), a 1 Nm increase in knee extensor strength (6-12 months) was associated with a 0.9 cm (95% CI, -0.5, 2.3) increase in hop distance. Similarly, every 1 Nm increase in knee flexor strength (6-12 months) was associated with a 0.3 cm (95% CI, -1.1, 1.7) increase in hop distance. Across other models, a 1 Nm increase in extensor or flexor strength was associated with a 0- to 0.3-point increase in KOOS score. CONCLUSION: There was minimal-to-no longitudinal relationship between changes in knee extensor or flexor strength and changes in triple hop or YBT performance, or self-reported function within the first year after a youth sport-related knee injury.