What's Rafa without his knees?

Something seemed just a little more off than usual when Rafael Nadal withdrew from the Olympics a few weeks ago. Nadal has a long history of knee ailments, but when he decided his game wasn't fit enough to play in the London Games, it had to make you wonder whether his latest setback was a little more serious than what we had heard and read.

That question was largely answered Wednesday, when Nadal renounced his participation in the season's final Grand Slam at the U.S. Open. Nadal, of course, hasn't played since his loss at Wimbledon, where an unknown Lukas Rosol unleashed a barrage of lethal groundstrokes to stun the Spaniard in five sets.

Now I can't help but wonder if we need to start talking about whether this is the beginning of Rafael Nadal's decline -- the end to the irrepressible punisher who pushes his opponents onto their heels more than any other player in the world. Nadal plays a brand of ball that is predicated on his movement, speed and force. He's never been swift and graceful like Roger Federer or light on his feet à la Novak Djokovic. Nadal moves as though he's playing running back. You take away the man's legs and, well, the rest is obvious.

Perhaps we're being a bit premature or hyperbolic here, and perhaps Nadal just needs more time to recover than he has in his previous knee injuries. Perhaps he'll come back and dominate the year-enders or Australia in January. Perhaps Nadal just isn't in match shape right now and doesn't want to suffer another Rosol-esque embarrassment. But we can safely say this: Nadal's fragile knees will never be fully able to hold up for the long grind of the season. He may feel great and strong in spurts. He may continue to dominate on clay and win more French Opens. But the days of Nadal being a legitimate threat for a full year have to be over.

So here's some sage advice, Rafa: Play a more judicious schedule. Approach the tennis calendar the same way the Williams sisters do. Don't get hung up on rankings or the spotlight or the rigorous demands of the mandatory Masters Series events. Pick either Indian Wells or Miami. Play only two out of the three Euro Masters events, then choose between Canada and Cincinnati in the lead-up to the U.S. Open. Finally, take the rest of the year off after New York. The final two Masters events and even the ATP World Tour Finals aren't worth the wear and tear. They just aren't.

Nadal is at the point in his career in which we're going to gauge him only on his Slam success. Even if he eschews some of the mandatory tournaments and his ranking takes a hit, so be it. He's still going to be better off than playing as one of the top-three-ranked players with a beaten-down body.

Nadal, who was hot on Federer's heels in his quest for the Grand Slam titles record, already has been slowed by the ascent of Djokovic. Nadal owns 11 major titles, six behind Federer, who just added to his total at Wimbledon. Six Slam titles is a major ask at this point in his career. At best, Nadal would need to win two a year for the next three seasons just to tie Federer, and that would assume Federer doesn't win any more. Nadal is 26 years old now, but an old 26. Much older than Federer was at that age. Nadal has endured far more wear and tear through the years and has far more mileage in his legs than any of the other elite players.

Can anyone really see Nadal playing close to Federer's level when he's Federer's age (31)? Sure, Federer is no longer in his prime, but he is still the No. 1 player in all the land. He's dealt with some back tightness and other niggling injuries, but they don't last. And that's why Federer is still this good at this stage. Nadal can't translate his game into a one-two serve and forehand punch. That's not his modus operandi. For Nadal to win, he needs to grind, then grind some more. Thus, he needs his legs. And his legs need healthy knees.

Rafa, we don't want this to be the beginning of your decline. We don't want to question your health and your knees every time you play. So take a step back to get your step back. Make the decision right now to play a more economical calendar. Withdrawing from the U.S. Open was a smart move. Because the next time you step on the court, we don't want to walk away asking ourselves who the heck Lukas Rosol is.