PWTorch reports that the injury is an arm/shoulder injury suffered during the main event of RAW. Del Rio landed hard towards the end of the match when he was flipped over the top rope. He started to favor his arm at this point. After he took a missile dropkick from Daniel Bryan, Del Rio slid to the corner, again favoring his shoulder. Del Rio could be seen talking to the ref towards the end of the match, and after it ended, he checked on Del Rio before calling the trainers from the back.
Sucks for Del Rio, but if he is to miss any time he won't be missed assuming his flirtation with the main event scene is done for now.