I'm not a doctor but I did date a girl once who was going to med school.
If it is a chest injury such as a torn muscle, a sling would be the right thing to do as it stablizes the arm. I did tear a muscle in my upper back/shoulder blade area and the doctor stapped my arm to my body and put in a sling. I had very littel pain after that and in a couple of days was able to move my arm around withut any pain.
If that is the case, I have no idea how long it will take for a torn chest muscle to be football ready.