It has been three days since Roger Federer was ushered out of the U.S. Open, falling in straight sets to a journeyman Spaniard who hadn’t beaten him in 10 previous attempts.

But the error-strewn performance by the 32-year-old Swiss champion remains a topic on the tournament grounds, in the locker rooms and player lounges and wherever tennis fans, competitors and commentators congregate.

Four-time U.S. Open champion John McEnroe said in a recent interview that he was so weary of the topic that he would allow just one question about Federer. He then proceeded to discuss the Swiss master at length.

Federer’s implosion here was so complete — so inexplicable for a player whose career has been defined by precision and grace — that it has prompted something akin to a collective howl for group therapy among those who love the sport.

“I don’t think there is one answer,” said McEnroe, 54, asked what he believed responsible for Federer’s haplessness against 19th seed Tommy Robredo, whose 7-6 (7-3), 6-3, 6-4 fourth-round victory ensured that Federer would finish the season without reaching the final of a single major for the first time since 2003.

“This is a combination of a lot of things,” McEnroe continued. “Guys aren’t as afraid of him. He’s not as sure of himself. Maybe he doesn’t want it as much as he did. I mean, when you’ve won 17 [major titles], presumably it gets harder and harder to get up for match after match. You beat a guy 10 times in a row, you’re going to pretty much assume you’re going to beat the guy, which is a mistake, as it turned out.”

For much of the past decade, Federer has set the standard for excellence on a tennis court.

In a peerless stretch from 2005 to 2010, he reached the final of 18 out of 19 Grand Slam events. His 17 major men’s titles and $77 million career earnings are both records. And the Roger Federer “brand,” in global marketing terms, is golden.

Forbes magazine in June deemed him the most powerful athlete in sports, based on an algorithm of annual earnings, print and broadcast mentions and social networking and marketability. Federer’s reputation is spotless; his comportment, sheer elegance. That explains why he boasts what’s regarded as the most impressive sponsorship portfolio in sports, with Nike, Rolex, Credit Suisse and Moet & Chandon paying him a combined $40 million a year to be associated with him.

Will the Federer brand be diminished if he slips from the top 10? The top 20?

More importantly, will Federer find the same joy in competing if his chief rivals rank above him, rather than below?

Andy Roddick long planned to retire once his ranking slipped to a personally intolerable point, bowing out soon after slipping from the top 20. Bjorn Borg quit at age 26, having lost the joy that had driven his brilliant but brief career.

Yet plenty of former No. 1s have played on for years, accepting their lost stature—Jimmy Connors, Andre Agassi and McEnroe among them.

“It comes down to how bad you want it,” said McEnroe, who competed eight years after winning his seventh and final major, retiring at 33. “How much does he love it?”