This, from one of baseball's more respected sources, Nick Cafardo:
Dan Uggla, 34, free agent — Uggla’s agent, Terry Bross, was trying to drum up business for an Uggla comeback at the Winter Meetings. A lot of Uggla’s decline may have had to do with an undetected concussion.
Would explain a lot. Not how the Braves didn't catch it, however.