His ankle hurts, according to the Herald [http://www.bostonherald.com/blogs/sports/red_sox/index.php/2009/03/18/ankle-injury-kos-youkilis-from-wbc/].
Now people, before you go on the stereotypical rants about the WBC and how it's dangerous and how the guy who dreamed it up should be shot, consider this:
(And no, it wasn't the celebrating that hurt Youk's ankle. He mentioned it "two or three days ago.")
I think that the cause of representing your country far outweighs the risk of getting injured. Teams should have no right to keep players out of the WBC, and it should be a honor to be asked to play. The only issue I see with it is that players need more time to get warmed up; they should report in early January to get ready.
But, other than that, the WBC is a great rallying point for countries that are struggling right now, and the players, whose job it is to entertain us, should be more concerned with playing for their country than the impact it will have on their team. And if they should be more focused on the WBC, so should we.