Rafa Nadal must be feeling somewhat left out.

As the Australian Open approaches - it starts on Monday - the Spaniard is the only one of the big four who is missing the latest must-have for the tennis superstar: a 1980s legend in the coaching team.

Andy Murray began the trend when he hired Ivan Lendl two years ago and now Novak Djokovic and Roger Federer have followed suit. Djokovic announced last month that Boris Becker has joined his team, followed a couple of weeks later by Federer's recruitment of Stefan Edberg. Nadal, meanwhile, is content to have his Uncle Toni, who has coached him since he was four years old, in his corner.

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The appointments to both the Djokovic and Federer camps are as surprising as they are intriguing. Murray's partnership with Lendl has proved to be an unqualified success, with the Scot's first grand slam title coming under the watchful eye of Lendl, followed by his maiden Wimbledon crown. It would, though, be folly to presume that Djokovic or Federer are simply copying the Murray model.

At the time of Lendl's hiring in late 2011, Murray had far more room for improvement in his game than either Djokovic or Federer currently do. The Scot had not won a major title and had definite weaknesses in his game. In contrast, Djokovic is the most rounded player on the circuit and, while Federer may be on the decline, he remains arguably the greatest tennis player in the history of the game.

So why have the pair gone for former players, neither of whom have significant coaching experience, rather than stick with the set-ups which had taken them so far? It is perhaps easier to answer in Djokovic's case than Federer's. The Serb has been coached by the Slovak, Marian Vajda, since 2006. Their partnership has been overwhelmingly successful with Vajda taking a teenage Djokovic from outside the world's top 40 to the top of the rankings, as well as securing six grand slam titles. Vajda was not a top player himself, though. He reached a career-high ranking of 34 and went no further than the third round of a grand slam tournament.

Herein lies the reason that Djokovic has brought Becker on board. There has been little mention of the German undertaking much coaching in the traditional sense, instead he will act as a mentor, just as Lendl has done so successfully for Murray. Over the last two years, if the Serb has had one weakness in his game it is the absence of that killer instinct in the latter stages of grand slam events which made him so deadly in 2011, when he won three majors in nine months.

Djokovic needs no help in reaching the semi-final stage of tournaments: so consistent is he against lower-ranked players that a trained chimp could get him this far. But it is the final days of big events that really matter; make wrong decisions at this stage and any chance of the title vanishes. Becker himself famously said: "The fifth set is not about tennis, it's about nerves."

Of the German's appointment, Djokovic said: "I need someone who can help me understand better what I need to do in particular situations, especially in the final stages of grand slams, someone to give me that mental edge. Boris can identify with me because he was in those situations himself so he knows what I'm going through."

The one omission on Djokovic's cv, though, is the French Open, so it is puzzling that he has hired a player who failed to win a clay court title.

Federer's appointment of Edberg was even more unexpected than the Djokovic/Becker combination. The Swiss believes that he has an 18th grand slam victory in him, however unlikely it may seem to outside observers. Edberg won six grand slam titles himself and was a leading proponent of serve-and-volley tennis, a style which Federer has employed with decreasing regularity as his career has progressed.

Most top athletes have an inherent 'show me your medals' snobbery, be it conscious or sub-conscious, whereby respect and a willingness to listen is granted far more quickly to someone who has been at the top level themselves.

It is virtually impossible to have an appreciation of the intangibles that can make the difference between victory and defeat without having had first-hand experience of elite sport. A former world-class athlete does not necessarily make a good coach, but when it comes to mentoring, they are the only people who meet the criteria.

Both Djokovic and Federer must be applauded for their willingness in seeking new ways to improve almost perfect games. Murray took a similar risk two years ago and has reaped the benefits. It will be interesting to see what impact, if any, Becker and Edberg have on the games of their respective charges.

A re-ignition of their '80s rivalry is unlikely to come to fruition from the stands, but it has certainly added an unexpected extra dimension. 014 could be an intriguing year.