He's saying that a stomach virus is keeping him out.  He wasn't going to win the AO anyway (he's not a player that can enter a tournament cold and win, at least, not off clay), but he's been out for an extraordinarily long time.

With this, Ferrer will overtake him to be ranked 4th.  I'm not sure that Rafa gets back to the top 4 by the French Open (I'm not sure the numbers are there).