Prolotherapy is effective in treating refractory tendinopathies, but inadequate clinical evidence exists to recommend its use as a treatment for acute or chronic, medial collateral ligament (MCL) injuries. The current case study documents an illustrative case of a rugby player who had a grade 2 sprain of the MCL and shows the clinical and radiological outcomes following injections of 15% dextrose combined with 0.2% lidocaine. In his case, the prolotherapy, together with an exercise therapy, lasted 3 wk. At the end of the 3 wk, the patient was pain free, with a full range of motion (ROM), and he was able to perform all rugby-specific movements. The mean duration for recovery with conservative treatment of isolated, complete tears of the MCL is normally 4-8 wk.