According to a recent report from the Wrestling Observer newsletter, 1/2 of the tag-team champions, Sheamus, is dealing with spinal stenosis.
Sheamus was absent from WWE from November 21st to December 1st. On television, it was explained he was merely taking time off in Ireland.
Spinal Stenosis
Spinal stenosis is a narrowing of the spine. It can lead to potentially career-threatening surgery in severe cases, such as with Edge and Steve Austin.
In less extreme cases, the conditioned can be rehabbed through a combination of medication and physiotherapy.