Just some basic things....
- when injured, do NOT stretch or work it in any way until the pain's gone
- the pain being gone does NOT mean the injury is healed. It means it's better enough that you can begin doing some PT on it.
- getting assessed by a physical therapist is a great idea. See what might be causing that spot to get undue pressure. Could be muscle activation issues, postural issues, functional problems, etc.....
- as you begin working it, getting deep tissue massage regularly to break up scar tissue and keep the new fibers oriented properly is a key, in my opinion.
- once you feel like you're all the way back, you gotta do some explosive movements. This, in my opinion, is where a lot of people don't take their training far enough. You have to re-teach the brain how to properly 'run' that muscle in a way to permit you to do what you want it to do. Tennis is very different than jogging, much more explosive movements, many 'unexpected'. If all your training is slow and steady stuff, the brain can literally 'forget' how to activate that chain of muscles fast enough to get sound and functional engagement. So something like plyometric work is a GREAT idea. Start easy, then build up.
When I injured my calf, once I got to the point where this was safe, I started by standing one step up from a stairwell landing, then jumping down onto the platform and landing evenly and softly with both feet. Would do that maybe 10 times, then move up a step, then another step, then another step until I was jumping down about 4-5 steps, trying to land like a cat, letting the knees and hips flex upon landing, trying to make as little noise as possible.
Then I did it again landing on one foot and alternating between the two. Only worked up about 2-3 steps that way.
Once I could do that, then I started jumping UP onto a box, or doing one legged hops over a small pillow, just slowly getting more aggressive with the movement.
Gotta retrain both the muscle tissue and the brain to accommodate the explosive movements tennis requires.
It's a crappy injury, good luck to all dealing with it.