From the Wrestling Observer:
We were told that Bryan was injured on 3/31 in his match with Sheamus at the Smackdown tapings in Fresno. Bryan was banged up and also bloodied up, and there was criticism of Sheamus in the match. PW Insider reported the injury taking place on 4/9 in Dublin, although that may have aggravated problems since the vague injury, the term “banged up” being used, was the term we were told after the Sheamus match and when the tour started.
One person who knew basically intimated that is was being kept a closely guarded secret and that banged up would be a nice, accurate but purposely vague way to put it.