Muscle tear. There are no specific studies showing that any one single nutrient would hurt or help for this injury. Maintain a well-balanced diet, making sure that you have adequate protein intake.
See below. I don't think there is any one food you should avoid as long as it provides nutritional value. Eating foods that are rich in anti-oxidants will be helpful as well as protein, fat and carbohydrates.
Good Question. I'm not aware of any studies or research looking at relationship of shoulder and rotator cuff symptoms and food. That said, for patients planning on a surgical procedure it does make sense to optimize your nutrition to promote healing.