Roger Federer is once again at the top of the tennis world and will be the No. 1 seed at the U.S. Open next week. Federer is the favorite to win for the sixth time, in part due to the absence of his longtime rival Rafael Nadal. Nagging injuries have forced him to miss the U.S. Open in addition to the 2012 London Olympics.
Federer and Nadal—though rivals for years—have never met in a U.S. Open final. Given Federer's age and Nadal's injuries, it is becoming increasingly likely that such a match will never occur. With Federer's resurgent year, a match against a healthy Nadal would make for the most exciting tennis of the summer.
This is not the first time an historic match has gone un-played in this rivalry. Five matches that should have gone down as legendary duels never happened at all.