Jon Wertheim: Rafael Nadal likely will not play again until Australian Open in 2013; more mailbag

It's tough to see Rafa pull out of the U.S. Open because you know he's in pain and discomfort. But on the other hand, we've seen this pattern before; if you chart his career on a graph every year, he tends to fall off a cliff in the summer. This isn't the first time that, come August, his knees have given him trouble -- his body isn't constructed to last a full playing season under his rough ...