I had this very injury in high school. The pile of bodies fell on me and my arm got caught and it bend the wrong way at the elbow. The pain was excruciating. Then my arm swelled up to 2 to 3 times normal size. I mean it looked like Popeye's forearm. I went to the hospital where they x-rayed it but there was no broken bones. Just everything stretched out of place. The Dr. gave me a shot and put my arm in a sling. A week later I was fine. I played a few plays in the following game. I am not saying Gallimore is going to be fine but I do know the injury can look a lot worse than it is and the pain can fool you into thinking it is serious. If there are no broken bones or torn ligaments, I can see Gallimore playing week 1.
If there are tears or breaks it will take a lot longer, maybe even the entire season.