Sore for forever, or sore until he drops by the doctor and the nurse shoots him up with cortisone?
I'm no doctor, but I've had biceps tendinitis before, as well as elbow (commonly known as "tennis elbow") and shoulder tendinitis, and it can be pretty damn painful. Doctors treated mine a couple of times with cortisone shots and several times with anti-inflammatory pills. It can stay sore for a long time, or only for a few days until the inflammation goes down to an acceptable level. With the treatment that these guys probably get, I'd be surprised if the DL stint wasn't over in two weeks. During that time, you just have to shut down your arm, but still get in your leg work to stay in shape. He might need a rehab start to tune back up.