Dave Meltzer revealed in the latest edition of the Wrestling Observer Newsletter that Sheamus is dealing with a significant injury which actually forced WWE Hall of Famers Edge and Steve Austin to retire:

Meltzer wrote, "While they said Sheamus was out of action last week because he was on a trip back to Ireland, he’s actually rehabbing spinal stenosis, which is not a good thing at all. Spinal stenosis ended the careers of Edge and Steve Austin"