Since Rome, Andy is not playing the same tennis as he used some months ago, problems of his back which trouble him when trying to serve is a huge disadvantage for him as serve is his besy quality. If he don't serve well, he can't play serve-and-volley style with the same effect as obviously the second shot will not be almost decisive in most of cases as he won't have the same position's advantage. Serve for Andy means a lot as this affect him all his play. Of course the American tried to do all his best for being fit here in U.S. Open but we have to take into consideration that he had a short period for that since his last game from Washington (USA) against Viktor Troicki where he didn't impressed.
Fabrice Santoro, looks ok from all points of view despite his age of 35, in last two years, Santoro had showed good tennis, he is a player who can play very well on faster surfaces as he had made many surprises in his career by beating top players. Another very important factor is that Andy Roddick allways had problems against Fabrice Santoro even if he leads 2-1 at head-to-head. All is all, Andy's various injuries will play a meaningful role in this game.