Superficial Digital Flexor Tendon (SDFT) injuries account for 30–50% of all musculoskeletal injuries in Thoroughbred racehorses, leading to substantial performance loss and early retirement [1]. The hierarchical structure of the SDFT consists of type I collagen-rich fascicles surrounded by an elastin-rich interfascicular matrix (IFM) and is crucial of tensile strength [2]. The mechanisms by which fascicle–IFM structural and compositional adaptations in response to athletic training and consequently for microdamage initiation remain poorly understood. Therefore, this study aims to construct multi-scale Finite Element Method (FEM) that captures SDFT mechanical behavior and microdamage mechanisms at both the fascicle-IFM and whole-tendon levels. Uniaxial tensile experimental data from Thoroughbred racehorse SDFT and constituent fascicles and IFM were performed and the results were integrated into FEM to simulate tensile response and fascicle–IFM interactions. In the proposed model, the fascicles along with the interspersed IFM bundles at the mid-metacarpal SDFT region were reconstructed, and hyperelastic material properties were assigned to both fascicles and IFM. Interfacial mechanics between fascicles and IFM were explicitly investigated using frictional sliding, cohesive traction–separation bonding, and contact-based interactions. These approaches enable systematic assessment of how inter-fascicle sliding and debonding contribute to strain localization and damage initiation under tensile loading. Initial simulations showed close agreement between FEM-predicted strain distributions and experimental tensile test data, with maximum strain discrepancies below 3%. The models successfully reproduced stress and strain fields observed experimentally up to the onset of damage initiation. These results indicate that microdamage localization and IFM failure patterns predicted by FEM correspond to experimentally observed failure modes. The developed multi-scale FEM framework provides a mechanistic basis for understanding SDFT microdamage progression and establishes a foundation for incorporating imaging-based reconstructions and viscoelastic behavior in future models. Ultimately, this approach can inform injury prevention and rehabilitation planning, in both equine and human tendon mechanobiology.