As was just announced on RAW, John Cena is OUT for the Unforgiven PPV in Cleveland in two weeks. The story goes that the injury is legit, and Cena is in bad shape. The following below is from WrestleScoop.com about the injury:
John Cena is currently working through a neck injury. The MSG match this past weekend was changed from a singles match to a tag match with Cena and Batista vs. Kane and Chris Jericho with Cena sitting on the apron for most of the match. Apparently Cena has been having these troubles with his neck for a few weeks now, likely before SummerSlam. One source reports that WWE brought John Cena in yesterday for some medical tests on his neck.
Until he is 100% cleared to wrestle, WWE is probably going to book Cena to protect him from getting hurt anymore until the Unforgiven pay-per-view match. We should have more details on Cena’s injury later on.