The Wrestling Observer Newsletter reports that the Randy Orton injury was a pre-existing injury. Orton has been protected in recent outings, since about December 19th, so that he would not have to do too much physically that would risk worsening the injury.
Orton could miss up to six months of in-ring time, causing him to miss WrestleMania 28. An official update from WWE should be available soon.
At this point, the plan looks to be to move one of the RAW matches to the SmackDown tour to help fortify the lineups starting tonight.