rest + light workouts is my advice. Depending on the injury I either pack it with ice after a workout (to reduce inflammation) and heat later to get blood flow to it. Anti-inflammation drugs help too (simple aspirin)
I'm sure the vets can tell you whether AAS will help. I know winny is rough on the joints so I would imagine that wouldn’t help with joint/tendon problems. I head deca does wonders for the joints so that may help. AAS stimulates muscle growth so I would imagine that would help with muscle tears but I do not think it would be a cure-all.