We described a 23-year-old male with no known medical illness, diagnosed with non-obstructive hypertrophic cardiomyopathy (HCM). The patient was scheduled for arthroscopic anterior cruciate ligament reconstruction surgery following an injury he sustained during football game few years ago, which he played leisurely. Prior to induction of general anaesthesia, the cardiac monitor showed abnormal deep T-wave inversion in leads II, III, aVF and V1–V6. The surgery was cancelled, and he was referred for further cardiac evaluation. Clinically, he was asymptomatic of heart condition with New York Heart Association Class 1. A further investigation revealed that he had non-obstructive HCM. A further investigation revealed that he had non-obstructive HCM with Modified Lee's cardiac risk assessment before non-cardiac surgery was 6.6% (moderate risk). We treated his left knee injury conservatively and advised him on being physically active based on the European Society of Cardiology Guidelines 2020.