<p>Frailty is a multidimensional condition encompassing physical, cognitive, and psychosocial domains; however, existing assessment approaches are often limited to physical domains or rely on clinical and laboratory-based measures, restricting accessibility and scalability. A comprehensive and quantifiable index is therefore needed to detect early functional decline in community-dwelling older adults. This study aimed to develop and validate a Physical Function-focused Frailty at Risk Index (PFFR-I) in 729 adults aged ≥ 65 years. The PFFR-I was constructed in two stages: a physical function composite was first derived as the composite z-score of grip strength, preferred gait speed, and physical activity; the final PFFR-I (ranging from 0 to 1, with higher values indicating poorer functional status) was then estimated from regression-predicted values incorporating multidimensional predictors, including demographics, comorbidities, patient-reported outcomes, gait parameters across multiple speed conditions, cognitive function, and quality of life. The PFFR-I demonstrated strong discriminative validity, with higher scores in individuals with a history of falls (OR = 4.80, <i>p</i> = 0.006). Quartile stratification revealed progressive functional decline, with the highest-risk group showing impairments in sleep quality, psychological stress, and 5-times sit-to-stand (AUC = 0.86). The PFFR-I may support early detection and targeted interventions.</p>