Your ACL, the anterior cruciate ligament in the knee, is very durable but isn't capable of self-repair. This is because the ACL does not have much blood supply to speak of. In order for bodily tissue to heal, it requires ample circulation of oxygenated blood. For this reason, more significant ACL injuries, such as tears, typically need surgery to regain the full function of the knee. It's important to consult with a doctor or knee specialist if you injure this part of your body. A thorough consultation and examination of the knee, and necessary imaging, can identify the severity of the injury. Your doctor will recommend treatment based on the "grade" of your injury.