Novak Djokovic returns from injury at this week's Shanghai Masters with the eyes of the tennis world on his form and motivation as his world number one spot comes under threat from Andy Murray.

The Serb has been a peerless performer in China, and when he won his third Shanghai Masters title last year he was putting the finishing touches on one of the best tennis seasons in history.

But after completing a career Grand Slam at the French Open in June, it has been a troubled period for the 12-time major winner who admitted he had lost his love for the game.

Djokovic fell in Wimbledon's third round and, tearfully, in the first round at the Rio Olympics, before going down to his bete noir Stan Wawrinka in the US Open final.

The Serb, who has spoken of "private issues", quit his usual residence in Monte Carlo to return to his native Belgrade, revealing that he wasn't "very well at an emotional level".

"I neither want to think nor to talk about the number one position, nor to win tournaments or Grand Slams," Djokovic told reporters in the Serb capital.

Wrist problems hampered him in New York. He then pulled out of this month's China Open in Beijing, where he was unbeaten in four appearances, with an elbow injury.

Djokovic will need to get quickly back into his stride as Murray, fresh from succeeding the Serb as the China Open champion late on Sunday, bears down on him in the rankings.

- 'Completely understandable' -

Murray beat Grigor Dimitrov 6-4, 7-6 (7/2) for his fifth title of the year after already winning his second Wimbledon crown and becoming the first back-to-back Olympic champion.

Murray had sympathy for Djokovic, his contemporary and sparring partner since their teenage years, saying his loss of motivation was "completely understandable".

"A lot of players have gone through that. It can happen at different stages," said the 29-year-old second seed. 

"When you achieve something that you've wanted to achieve for such a long time and put so much effort and thought into that, and come close a number of times and not quite done it, I think when you finally do it, you feel incredible for a number of days afterwards. 

"But there can be a low after that. It would be completely understandable to have those feelings. I'm sure a lot of players have experienced that at different stages after big wins in their career. I think it's quite normal."

One possible obstacle in Djokovic's half of the draw is Rafael Nadal, although the 14-time Grand Slam-winner is fighting to prove he's still a force at the top of the game.

With two titles to his name this year, plus fourth place at the Rio Olympics, the 30-year-old Spaniard is heading for his smallest trophy haul in a season since 2004.

'Stanimal' Wawrinka, the world number three and US Open champion, is in Murray's half and is returning to action after his stunning loss in the St. Petersburg final to rising German star Alexander Zverev.

And Australia's often-controversial Nick Kyrgios comes to Shanghai in hot form after winning his third tournament of the season at the Japan Open on Sunday.

Source: AFP