(CNN) -- Roger Federer will not feature in a Grand Slam final in the same calendar year for the first time since 2002, after he was knocked out of the U.S. Open by Spain's Tommy Robredo.
The winner of 17 Grand Slam titles, including five in New York, suffered a straight sets defeat in his fourth round match at Flushing Meadows, losing 7-6 (7/3) 6-3 6-4 late Monday.
The defeat denied the Swiss star, arguably the finest player to have played the game, a quarter-final showdown with long-time nemesis Rafael Nadal, after the in-form Spanish star beat Germany's Philipp Kohlschreiber 6-7 (4-7) 6-4 6-3 6-1.
Robredo had never beaten Federer before their latest rain-delayed encounter on the Louis Armstrong Stadium court. But with 43 unforced errors to his name and only two break points converted from 16, the former world number one looked unlikely to extend that run.
"I'm going to feel like I beat myself," Federer told reporters after the match. "It was up to me to make the difference and I just couldn't.
"I self-destructed, which is really disappointing. When things came to the crunch I just couldn't do it. It's frustrating."
Robredo, by contrast, was full of confidence as he hit 70% of his first serves and sent numerous forehand winners whistling past his illustrious opponent.
"I'm delighted. It's unbelievable. The difference is I won the break points today," said Robredo.
With the ignominy of another early exit from a Grand Slam tournament, Federer, whose ranking has slipped to an unfamiliar No. 7, will face renewed speculation about his future.
At 32, some question whether he can arrest the recent decline in his fortunes -- his last major title was at Wimbledon in 2012.
"Roger is in a very vulnerable state. He's in a vulnerable position because he's moved down to No. 7 now," said legendary coach Nick Bollettieri in a recent interview with CNN.
"Remember Pete Sampras went through a tough period. Fortunately for Pete he won a big one before he left the tour."
But with younger rivals Novak Djokovic, Rafael Nadal and Andy Murray improving all the time, Federer will be acutely aware that his window of opportunity is rapidly closing.
He has even experimented with a larger racquet head in a bid to find a solution to his on-court problems.
And for Bollettieri, who has coached a number of former Grand Slam champions including Andre Agassi, there's a real concern that an underwhelming end to his career could undo the Federer legacy.
"It would be a shame if people forgot who he was," he said. "Look at what he brought to the game. He brought class. He lived a beautiful private life.
"He's quiet. He's always respectful of the sport. He's respectful of his opponents. You don't find too many people who represent life, whether it be business or sports, like this guy."