DEPENDING who you listen to, Novak Djokovic is either physically or mentally shot and has no chance of defending his US Open title here this fortnight.

The Serb, beaten early at Wimbledon and the Olympics and troubled by injury and personal problems this summer, did little to suggest he should be favourite with a patchy four-set victory over Jerzy Janowicz of Poland at Flushing Meadows on Monday night.

The left wrist issue that he picked up just before Rio has been improving, he says, but he also required treatment to a right elbow problem early in the match before finally pulling away in the fourth set.

Rumours of trouble in his personal life continue to dog Djokovic but the Serb remains the world No.1 and the man most likely to deny Andy Murray in his quest to win a fourth grand slam title.

Coach to the stars, Nick Bollettieri, the man responsible for a string of world No.1s from Andre Agassi and Jim Courier to Monica Seles and Maria Sharapova, said it was too early to write off Djokovic.

“He certainly [looks] a little different,” Bollettieri told Herald Sport. “I don’t see the confidence that he had but don’t discount Djokovic.

“He and Agassi are two of the greatest returners ever and when you don’t know what’s going on behind the scenes it’s tough to say anything.

“Today, with the depth in tennis far deeper than the 70s, 80s and 90s, the penalty of being the best in anything in the world is that you can’t let up.

“Once you lose the fear factor – and he has had a fairly indifferent summer – then people look forward to playing you.

“I wouldn’t discount him but Murray is playing unbelievable and there are others, [Kei] Nishikori, [Milos] Raonic, [Marin] Cilic behind.”

It is less than three months since Novak Djokovic completed the career grand slam by winning the French Open for his fourth consecutive grand slam title.

Having lost in the third round at Wimbledon soon after, he won the title in Toronto only to follow it with a first-round loss to Juan Martin del Potro at the Olympics, where the left wrist issue flared up.

The good news for Djokovic, who plays the Czech, Jiri Vesely in round two today, is that he felt like he was improving as the match went on against Janowicz.

“I thought I did well in the third and fourth sets to bounce back from the dropped second set,” he said.

“It's an opening match, night session. After all I've been through in last couple of weeks, it's pleasing, of course, to finish the match and win it. I'll try to look positive and just think about the next day.”