Roddick withdraws from Masters Cup

I read in the news today that Andy Roddick has officially withdrawn from the Masters Cup. Apparently he has been having some back spasms, and he doesn't think he'll be well enough to play this weekend. I also discovered that Lleyton Hewitt had also withdrawn from the event, which means that 2 of the top 4 players in the world won't be competing. It should still be fun to watch, though. I'd love to see Federer play Nadal in the final. They haven't played each other since the French Open, and, in my opinion, Nadal had the advantage due to the clay surface. A match on a different surface will be interesting to say the least.