NEW YORK: Plagued by back trouble and the declining influence brought on by advancing years, Roger Federer heads for the US Open with his game and legacy, if not his famed confidence, in crisis.

The 17-time Grand Slam title winner is at a crossroads as he prepares for his 14th US Open.

A five-time champion at Flushing Meadows from 2004 to 2008, the 32-year-old Swiss finds himself at seven in the world – his lowest ranking since October 2002 – after a tortuous summer.

His second round loss to Ukraine's world number 116 Sergiy Stakhovsky at Wimbledon was his worst Grand Slam defeat for a decade and ended a run of 36 successive quarter-final appearances at the majors.

Then followed the bizarre decision to play low-profile claycourt events in Hamburg and Gstaad which ended in shattering losses to unheralded Federico Delbonis and Daniel Brands, both outside the top 50.

There was even a brief flirtation with a larger racquet as Federer scrambled for a recovery.

The statistics are conspiring against the former world number one whose last US Open final appearance ended in defeat to Juan Martin Del Potro in 2009.

His great hero Pete Sampras won his fifth and final US Open in 2002 when he was 31 and promptly quit the sport, a punch-drunk second round exit at Wimbledon having already warned him of the dangers of over-staying his welcome.

Meanwhile, Federer's great rivals – Novak Djokovic, Rafael Nadal and Andy Murray – all seem comfortably to have the measure of him.

World number one Djokovic trails 16-13 in their career match-ups but the Serb, who was the 2011 champion in New York and runner-up in 2010 and 2012, has won seven of their last 10 meetings.

Nadal leads 21-10 and has also won seven of their last 10 clashes, including all three in 2013.

Murray, the defending US Open champion, leads Federer 11-9 and have split their last 10 clashes.

Federer, however, insists he is unconcerned about his predicament, shrugging off his lowly ranking and preferring to accentuate the positives gleaned from taking a set off Nadal in their Cincinnati quarter-final last week.

“It doesn't change anything for the US Open. As long as you're either in the top 4 or the top 8, I think at this point that's what matters,” said Federer.

“Rankings are not what lead me. It's about getting my game back on track, and that's what I'm doing well. So that's what's exciting right now.”

The Swiss will discover how tricky his New York path will be when the draw is made later Thursday, but his humble seeding means he could face any of the top three as early as the quarter-finals.

He insists his back problem is not the restriction that it has been in recent weeks, even if, deep down, he remains to be totally convinced.

“I believe when I can walk and I can hit decent, you never know. Sometimes miracles happen, like last year at Wimbledon (when he beat Murray to win his most recent Grand Slam title). You get a bit lucky or you heal well, get the extra day off, and all that stuff.”

AZARENKA THREAT

World number one Serena Williams enters the US Open as a heavy favourite to defend her title, but second-ranked Victoria Azarenka leads a host of rivals looking to dethrone her.

Williams is seeking her 17th Grand Slam singles crown and fifth US Open title, which would move her one shy of Chris Evert's Open-era record for most titles at the year's final major event on the Flushing Meadows hardcourts.

“I'm definitely prepared. I'm definitely ready for New York,” Williams said. “I definitely had more matches than I could want, but I'm definitely prepared for the US Open.”

The 31-year-old American has been on an amazing run over the past 14 months, going 77-4 and capturing last year's Wimbledon, London Olympic and US Open titles, plus this year's French Open crown.

But two of those defeats came at the hands of Azarenka, in last February's Doha final and last Sunday at the WTA final in Cincinnati by a score of 2-6, 6-2, 7-6 (8/6).

It was only the third victory for the 24-year-old from Belarus over Williams but with the two having won seven of the past nine Grand Slam titles, it sets the stage for a potential rematch of last year's US Open final.

“It would be totally different circumstances,” said Williams, who also beat Azarenka in this year's Rome final. “It's just a new event. You just got to go in there with a fresh mind.”

Williams will go into the Open without a win streak such as she had the past few Grand Slam events.

“It makes me more relaxed and almost happy that I lost because now I don't have to worry about every day someone asking me about some silly winning streak,” Williams said. “So maybe it was for the best.”

Williams also finds herself in a cordial rivalry, appreciating Azarenka off the court as a friend and on the court as an adversary.

“She's so competitive on the court, like an animal, and I'm the same exact way, like my dad described me as a pitbull,” Williams said.

Williams is looking for her ninth title of the year after triumphs at Brisbane, Miami, Charleston, Madrid, Rome, Roland Garros, Bastad and Toronto.

But she has proven vulnerable in Grand Slams, falling to compatriot Sloane Stephens in the Australian Open quarter-finals and Germany's Sabine Lisicki in the fourth round at Wimbledon, but completing her title run on Paris clay with a victory over Russia's Maria Sharapova.

Sharapova would have been the third seed at the US Open but she withdrew from the tournament on Wednesday, citing right shoulder bursitis.

As a result, Poland's Agnieszka Radwanska becomes the third seed, followed in order by Italy's Sara Errani, China's Li Na, Denmark's Caroline Wozniacki, Czech Petra Kvitova and Germany's Angelique Kerber.

Azarenka, the reigning Australian Open champion, says she has learned from past losses to Williams.

“Every time we play, I face a big challenge, my biggest opponent, and that's what I want to go through,” Azarenka said.

“I had tough losses before against her, but I feel like I learned from those losses, and it helps me improve. I feel like I'm playing better and better. I'm reaching for the new level that I want to be at, physically, mentally, tennis-wise and that's the progression that I'm really the most excited about.”

Azarenka took confidence from rallying to beat Williams in the Cincinnati final, but says the American will be the favourite on home soil.

“I will not be a favourite,” Azarenka said. “She is No.1 in the world. She is a great champion, and she's defending champion, so she's going to be a favourite.

“About who's second favourite, third favourite, I don't really care about that. But I think it's a great boost of confidence to go to the US Open, great week to go through matches back to back. Tough matches are also important for me to feel like I'm back competing at the same level constantly and consistently. So that's what I'm most excited about."