What exactly A-rod has to do in order to seal his spot at shanghai? would a 3rd rnd performance still make him among top 8??
At this point, it doesn't really matter all that much what Roddick does, he'll be hard to catch even if he didn't play. To be out, Del Potro must pass him, which is possible, but also two of Simon semi, Ferrer semi, Blake final, Wawrinka final, Gonzalez win, Tsonga win, or (maybe) Verdasco win or Nalbandian win. That's with Roddick not even playing.
Realistically, he's safe enough that there is little difference between not playing and a third round. It would mathematically clinch it, if it's not already clinched by others going out.