It was announced today on WWE's The Bump that he has a grade 2 MCL sprain, which means he will be off TV for a while.
The storyline injury occurred this past Monday when Edge was attacked by The Judgment Day. As was previously noted here on WrestlingNews.co, the attack angle appeared to be WWE's way to write off Edge for a while. Edge is not wrestling a full-time schedule so it looks like he will be taking several weeks or months off.
In the meantime, it looks like Rey Mysterio will have to battle against The Judgment Day on his own or he will need to find some help. You can listen to the announcement about Edge in the video below.