CUE zither music.

And let the search for The Fourth Man begin. The clumsy reference to The Third Man and its distinctive soundtrack can not obscure the fact that there is a vacancy in the top four of world tennis.

Rafael Nadal's long-term injury has left Novak Djokovic, Roger Federer and Andy Murray beyond the chasing pack. Murray, for example, has 1500-plus ranking points more than David Ferrer in fifth spot and almost 6000 more than the world No.10 Richard Gasquet.

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The top three have a grand slam history of multiple semi-finals and finals, with Federer having won 17 majors, Djokovic five and Murray one. The only major winner outside the top three with a semblance of a chance in Melbourne is Juan Martin del Potro, who won the US Open in 2009 before being hampered by a succession of injuries. He leads the candidates for the position of The Fourth Man, though, even though he is placed at No.7 in the rankings.

The chasing pack to the Big Three can be loosely categorised as The Usual Suspects and The Young Guns. Del Potro heads the former group, completed by Ferrer, Tomas Berdych and Jo-Wilfried Tsonga.

The 24-year-old Argentine has achieved the most difficult part, winning a grand slam, and has the game to prosper on the hard courts of Melbourne. Ferrer, the 30-year-old Spaniard, can only be cast as an irritant, a possible semi-finalist rather than a potential winner, as his fitness may be unlimited but not his game. He does not have the capacity to beat two top-three players consecutively.

Berdych is the most intriguing candidate. The 27-year-old Czech has proved at Wimbledon and at Flushing Meadows that he can have the measure of Federer. He also beat Djokovic in the semi-final of Wimbledon 2010. His heavy serve and groundstrokes can create problems for the best but it is difficult to see him having the focus and fitness to win seven consecutive big matches in the heat of Melbourne.

Tsonga will be returning to the scene of his greatest moment and biggest disappointment in tennis. The 27-year-old Frenchman was beaten in the final in Melbourne in 2008 and has never come as close to a grand slam title since. Immensely athletic, strong and gifted, with more than a degree of technique, the world No.8 has become increasingly frustrated at his inability to win a grand slam.

He eschewed coaching help for more than a year after ending his collaboration with Eric Winogradsky but, late last year, recruited Roger Rasheed, the Australian coach. Rasheed is an excellent motivator who also places emphasis on physical fitness. Tsonga needs to improve in both these areas to challenge the Big Three on a consistent level but he has the game to cause trouble at a grand slam.

His difficulty is that he craves a grand slam triumph and that needs a level of sustained excellence – both physical and mental – that is the preserve of the top three in the rankings. There is improvement in Tsonga but it will have to be substantial if he is to lift the trophy in Melbourne – although he is capable of overwhelming anyone in the draw in a one-off match. Federer, for example, will recall with a wince a day at Wimbledon when a two-set lead was washed away by a storming display from the Frenchman.

The Young Guns are a motley bunch, marked with potential but pockmarked by frailty. The most intriguing is Bernard Tomic, the 20-year-old Australian, who showed this month that he has the game to prosper at the highest level when beating Djokovic in the Hopman Cup. This tells one story but so does his ranking of 43rd in the world when he was in the top 30 last summer.

Tomic is a difficult personality who has been involved consistently in matches where he has been accused of "lack of effort". He has to mature physically and in his focus before he will be anywhere near the top level but, again, he is capable of the one-off upset.

Other youngsters with potential include Milos Raonic, the 22-year-old Canadian who hit more than 1000 aces in 2012 and has a decent game to back up this heavy artillery. Jerzy Janowicz, a 22-year-old Pole, has made substantial progress, rising from outside the top 200 to 26th in the world in a year. His major breakthrough was at the Paris Masters where he lost in the final to Ferrer after defeating Murray, Janko Tipsarevic, Marin Cilic and Philipp Kohlschreiber.

The other young pretenders include Grigor Dimitrov, the 21-year-old Bulgarian nicknamed Baby Federer, who lost in Brisbane to Murray after a good run.

However, The Young Guns and The Usual Suspects will have difficulty rewriting a script that has run almost unchanged since Djokovic won the Australian Open in 2008. The Big Three are the strongest of favourites, Del Potro an outside bet.

There is the capacity for a dramatic twist in true Hollywood style but the reality may be that The Fourth Man will only play a supporting role to a triumphant performance by one of The Big Three.