World Tour Finals: Will Novak Djokovic reclaim the No. 1 ranking from Andy Murray?

    Story highlights

    • World Tour Finals start Sunday in London
    • Djokovic can return to No. 1
    • Murray has never reached the final at the event
    • Roger Federer and Rafael Nadal absent

    (CNN)Andy Murray this week ended Novak Djokovic's two-year reign atop the rankings in men's tennis but the Scot's stay at No. 1 could be a short one -- and he knows it.

    "I might as well try and enjoy it because I could lose it at the tour finals and never be there again," Murray told reporters, referring to the year-end championships, which start Sunday in London.
      Indeed, Djokovic can regain the top position on Nov. 21 and finish the season as No. 1 for the third straight time with a strong showing at the World Tour Finals.
      The 29-year-old has certainly fared well at the O2 Arena, winning a record four consecutive titles and if he makes it five in a row while winning at least two of his round-robin matches, Djokovic is guaranteed to seize back the No. 1 ranking from Murray.
      Djokovic, however, has struggled since winning the grand slam he craved, the French Open, in June.
      A loss of motivation, personal issues and injuries have slowed the Serb, who became the first man in 47 years to claim four straight majors when he defeated Murray in the final at Roland Garros.
      His ties to a "spiritual guru" and former Spanish pro, Pepe Imaz, raised eyebrows, especially since his usual coaches, Boris Becker and Marian Vajda, didn't accompany him at the recently concluded Paris Masters, where Djokovic relinquished the No. 1 ranking.
      The mantra of Imaz's "tennis group" in Marbella is: "We truly believe love is the way to live life."
      Becker and Vajda are expected to return to the Djokovic camp in London and helping Djokovic is that, seemingly, he drew the easier group in the eight-man tournament, having never lost to group rivals Milos Raonic, Gael Monfils and Dominic Thiem. But then Djokovic had never tasted defeat to Marin Cilic in 14 matches -- before losing to the Croat in the City of Light.
      Here is a break down of the groups.
      John McEnroe group:
      Andy Murray. The Scot became a dad this year for the first time, which he says has been instrumental to his success in 2016 as he won a second Wimbledon title and retained his Olympic crown. But it was after the Olympics that he truly stormed to the No. 1 ranking, despite a blip at the US Open. Murray has won 19 straight matches, dropping a mere four sets during the streak. He is bidding to make the final at the year-end championships for the first time.
      Murray surely won't be taking his group rivals lightly: Stan Wawrinka has beaten Murray in three of their past four meetings, with Cilic and Kei Nishikori getting the better of Murray in August and September, respectively.
      Stan Wawrinka. The Swiss is adamant that he shouldn't be part of any "Big Five" in tennis due to his lack of consistency -- compared, that is, to Djokovic, Murray, Roger Federer and Rafael Nadal. Yet Federer's fellow Swiss continues to prove he is a man for the big occasion, winning a grand slam for three straight seasons. When he toppled Djokovic in the US Open final, he did so from a set down. Wawrinka's lovely -- and bulldozing -- one-handed backhand garners much attention but his forehand is, too, one of the most powerful around.
      Kei Nishikori. The Japanese star put in a lackluster performance against Murray at the Olympics but turned it around in New York, outlasting Murray in a pulsating five-setter in the quarterfinals. Injuries continue to hamper Nishikori -- he retired at Wimbledon and then at home in Tokyo -- yet when the Japanese shot-maker is fit and on his game, he possesses the weapons to beat just about anyone. And if matches go to a deciding third or fifth set, his career record is stellar, despite a reverse to Jo-Wilfried Tsonga in Paris: 99-27.
      Marin Cilic. The Croat, the 2014 US Open winner -- he beat Nishikori in the final -- is arguably the second most in-form player at the event after Murray. He won the Swiss Indoors over Nishikori and reached the semifinals at the Paris Masters, one day after finally ending his seismic slump against Djokovic. Especially on faster surfaces the 6-feet 6-inch Cilic is a threat: He has a huge serve, impressive two-handed backhand and isn't afraid to play at the net. Cilic's forehand could be the key, though. Prone to wavering, when the forehand is stable it spells trouble for his peers.
      He is the latest player at the World Tour Finals to play in the Davis Cup final post London.
      Ivan Lendl group:
      Novak Djokovic. Can Djokovic replicate his early season performances when he plays at the O2 Arena? His fans hope so. Onlookers might get a feel for Djokovic's form when he challenges Thiem to open the singles on Sunday. Djokovic's much publicized struggles may lead some to wonder if his most dominant stretch of tennis is behind him, although even if the Serb falters at the World Tour Finals, a better gauge would be at January's Australian Open, where he has won the title five times in six seasons.
      Milos Raonic. The Canadian, fourth in aces in 2016, began his campaign with a bang in Melbourne, making the semifinals. Some, too, would argue that if he hadn't sustained an injury he would have ousted Murray after holding a 2-1 lead in sets. Raonic shone again at Wimbledon by advancing to a first grand slam final -- Murray beat him again -- but the injuries have hit him recently. Raonic pulled out of his semifinal against Murray in Paris with a thigh injury and said last week he was unsure of competing in London. Belgium's David Goffin is the first alternate.
      Gael Monfils. Ever the showman, Monfils was more focused on court this year -- his bizarre antics against Djokovic at the US Open notwithstanding -- and his spot at the year-end championships for the first time is the reward. The Frenchman managed to qualify for London even after missing the French Open due to illness and suffering physically at other stages of the season. Monfils reached the quarterfinals or better at 10 tournaments, highlighted by a semifinal run in New York and final in Monte Carlo.
      Dominic Thiem. Just 23, Thiem is the youngest member of the field. His has been a tale of two seasons. Up until the week before Wimbledon the huge-hitting Austrian compiled a 48-12 record, beat the likes of Federer and Nadal and made his first grand slam semifinal at the French Open. But his record from the start of Wimbledon through the Paris Masters slumped to 11-10. Why the dip? The issue for Thiem appears to be playing too much: No one inside the top 20 has played more than Thiem's 27 tournaments this year.