The word going around WWE is that John Cena is suffering from a back injury.
Reports indicate that Cena is suffering from a few bulging discs, which can be very painful and might require surgery.
Not much more is known about the injury at this time and the severity is hard to assess.
Nonetheless, it does appear that Cena’s condition is the reason Cena will not be wrestling WWE Champion Sheamus at the Royal Rumble.