Treatment. On average, it takes six weeks for a MCL injury to heal. The initial treatment for most grade 1, 2 or 3 MCL tears focuses on reducing the pain and inflammation in the knee while immobilizing the knee to keep it stabilized. A grade 2 tear can take from two to four weeks to heal. 2  A grade 3 tear usually takes from four to eight weeks to heal, unless it is associated with damage to the ACL, in which case the recovery time may be longer.