Disc desiccation in 26 year old male.

My friend developed left leg numbness while he walked or stood at a place for more than 15 min since last 2 months. He goes to gym and lifts upto 70-80kgs. He got an MRI scan done which stated "Disc desiccation with postero-central disc protrusion L5-S1 level causing moderate spinal canal stenosis with compression of thecal sac and traversing nerve roots ( L>R)". Earlier he did not have noticeable lower back pain but yesterday night he experienced pain in lower back while sleeping which reduced after he walked for a while. He is currently working as an intern doctor so has a moderately active lifestyle. What should he do now to prevent further progress of the disease and what are the treatment options for his age and lifestyle? Should he do stretching exercises or not ? Will physiotherapy be helpful for his condition?