The current study endeavored to replicate the approach to sports-related concussion management adopted by some community-based sporting organizations by examining the diagnostic efficiency of CogSport and ImPACT in athletes without baseline test data and assessed only once postinjury. Recently concussed nonelite-level rugby union players (N = 51) were tested within 72 hours of sustaining a concussion and were compared to nonconcussed matched controls (N = 41). Demographic information and history of recent concussion were also collected. Logistic regression analysis and receiver-operating characteristic curve analysis were conducted to evaluate the most accurate scores at identifying group membership. Overall, the classification accuracy of CogSport and ImPACT represented only very minimal improvements over a demographic-only (age, estimated premorbid Full-Scale IQ, and number of previous concussions) model. Positive predictive power and negative predictive power of composite scores were modest. The ImPACT postconcussion symptoms total (severity) score was most accurate at classifying concussed athletes. Where neuropsychological tests are utilized on a single occasion postconcussion and in the absence of baseline testing, postinjury testing does not improve diagnostic utility beyond the demographic model. These results do not validate this approach as a useful method of managing sports-related concussion.