The aim of this study is to investigate if self-reported activity level or knee functions are influenced by subject characteristics, level of competition and history of knee injury. Cross-Sectional study using questionnaires distributed at a personal visit. One hundred and eighty-eight (65 women) amateur football players in 10 football clubs from each division below national level participated in the study. Self-reported Tegner Activity Scale, and the Knee injury and Osteoarthritis Outcome Score (KOOS) are the main outcome measures. Older age, female gender and lower level of competition (football division) were independently associated with lower self-reported Tegner Activity Scale (P < 0.001). Subjects reporting history of knee injury had significantly worse KOOS scores (P < 0.001 for all subscales). In future studies, a clear description of how the Tegner Activity Scale was administered is recommended. We suggest that self-reported Tegner Activity Scale scores should be adjusted for age, gender and level of competition. In amateur football players, KOOS scores do not need adjustment for age and gender.