Generation game: The kids threatening Roger Federer, Novak Djokovic, Andy Murray and Rafael Nadal at the top of tennis

The era of top-four domination could be coming to an end. As the new season opens, Paul Newman assesses the youngsters hot on the heels of Murray and Co

For the last eight years the rest of men's tennis has watched in a mixture of admiration and frustration as four players have dominated the major competitions. At the dawn of another Grand Slam season, however, the hopes of a new generation of players are rising at last.

With Roger Federer reaching his 32nd birthday this year and doubts growing over Rafael Nadal's future following the Spaniard's withdrawal from next week's Australian Open, younger players such as Milos Raonic, Bernard Tomic and Grigor Dimitrov might feel that now is the time to make their move. While Novak Djokovic and Andy Murray may still be in their prime for several seasons to come, there is likely to be room at the top alongside the two 25-year-olds in the near future.

Nadal, who has not played since Wimbledon after a recurrence of his knee problems, is certain to be out of the top four by the end of the Australian Open. He will plummet further down the world rankings if he is not back and winning tournaments by the start of the clay-court season.

Federer, meanwhile, may also struggle to keep his place in the top group, especially as his schedule for 2013 has indicated a shift in priorities. The world No 2 will not play anywhere for seven weeks between Indian Wells in March and Madrid in April, meaning that he will miss the Masters Series tournaments in Miami and Monte Carlo.

The stranglehold of the big four in the Masters Series – the next level of competition below the Grand Slam tournaments – could be over already. Between them Federer, Nadal, Djokovic and Murray had won 17 Masters titles in succession until David Ferrer ended the run in Paris two months ago.

The grip of three of the Fab Four on Grand Slam trophies has been even tighter. Following Marat Safin's victory in the Australian Open of 2005, only one of the subsequent 30 Grand Slam tournaments – the 2009 US Open, in which Juan Martin del Potro triumphed – was not won by Federer, Nadal or Djokovic. The 31st and most recent tournament in that sequence, last year's US Open, was won by Murray.

Statistics show that today's players tend to peak later in their careers than they have in the past, probably as a consequence of the greater physical demands of the modern game. However, it is also true that most Grand Slam champions win their first major titles in their early twenties. The chance of Grand Slam glory may already have passed by some of the recent mainstays in the world's top 10, such as 30-year-old Ferrer and even the 27-year-old Jo-Wilfried Tsonga and Tomas Berdych.

There are no teenagers currently in the world's top 100, but there are players in their early twenties for whom the future is looking bright. Next week's Australian Open, which is the Grand Slam tournament where form is often the most difficult to predict and which has produced more than its share of surprise winners over the years, could see the door open for them at last.

Seven players from the next generation who might join the elite

Milos Raonic; Canada

Age: 22 World ranking: 15

In the last two years no man has been more frequently tipped for the top. The "Maple Leaf Missile", whose family moved from Montenegro to Canada when he was three, stands 6ft 5in and delivers thunderbolt serves. He hit 1,002 aces in 2012 and won 82 per cent of points on first serve. Nevertheless, there is plenty more to Raonic's game, as he showed with victories over Andy Murray in Barcelona and Tokyo. He has won three titles but has yet to make a major impact at a Grand Slam tournament, his best runs having been ended in the fourth round by David Ferrer in Melbourne two years ago and by Murray in New York last year. However, time is on his side.

Grand Slam potential *****

Bernard Tomic; Australia

Age: 20 World ranking: 64

Tomic announced his arrival as a major contender with a run to the Wimbledon quarter-finals two years ago, but his career has been dogged by controversy. Coached by his outspoken father, Tomic has been involved in a series of disputes within tennis, while his love of fast cars has landed him in trouble with the police. When he gives his all on court, however, he is the most exciting talent to have emerged in men's tennis in recent times. The former world junior No 1, who has been the youngest player in the world's top 100 for two years, has a wonderfully languid style and loves the big occasion, as he showed when beating Novak Djokovic in the Hopman Cup in Perth last week.

Grand Slam potential *****

Ryan Harrison; United States

Age: 20 World ranking: 68

The second youngest player in the world's top 100 (after Bernard Tomic), Harrison has a huge forehand and a powerful serve, but here have been occasions when his temperament has let him down. He has a reputation as a hothead and when he gets angry his game can suffer. He comes from a tennis family, started playing the game at two and has been based at Nick Bollettieri's academy since 2008. He reached three semi-finals last year, including two on grass, at Eastbourne and Newport. Although he has improved his year-end world ranking for the last five years in a row, there is a danger that the American public, desperate to find their next male Grand Slam singles champion, will expect too much too soon.

Grand Slam potential ***

Jerzy Janowicz; Poland

Age: 22 World ranking: 26

Twelve months ago Janowicz was ranked No 222 in the world and had never played in the main draw of a Grand Slam tournament. He beat Simone Bolelli and Ernests Gulbis on his Grand Slam debut at Wimbledon and capped a year of outstanding progress by reaching the Paris Masters final in November, beating four top 20 players in Andy Murray, Janko Tipsarevic, Marin Cilic and Philipp Kohlschreiber before losing to David Ferrer.

Standing 6ft 8in and weighing more than 14st, Janowicz has the big-hitting game to match his physique. He strikes a huge forehand, enjoys playing on all surfaces and looks to have plenty of scope for improvement. He started playing tennis at five and grew up idolising Pete Sampras.

Grand Slam potential ****

Grigor Dimitrov; Bulgaria

Age: 21 World ranking: 41

Eyebrows were raised in 2009 when Dimitrov, then the world No 361, was awarded a wild card at Queen's Club, but the judgement of Chris Kermode, the tournament director, has since been vindicated. An elegant player with a style often compared to Roger Federer's, Dimitrov underlined his potential at last week's Brisbane International, where he beat Milos Raonic, Jürgen Melzer and Marcos Baghdatis en route to his first career final before losing to Andy Murray. Dimitrov, who reached the semi-finals at Queen's last summer, was based in France for four years but at the end of last season moved to Sweden, where he is now coached by Mikael Tillstrom.

Grand Slam potential ****

Kei Nishikori; Japan

Age: 23 World ranking: 18

If Grand Slam titles were decided on talent alone Nishikori would be a very short price to make his breakthrough soon. The most successful male player in Japanese history has an inventive game and a wonderful touch. Doubts remain about his physical strength, but he has recovered from injury problems to enjoy his best run yet. Nishikori went to Nick Bollettieri's Florida academy when he was 14 and could not speak a word of English. He won his debut title at Delray Beach at 19 but his career was then derailed by a serious elbow injury which required surgery. His second title came four and a half years later, in October 2012, when he became the first home player to win the Japan Open.

Grand Slam potential ***

David Goffin; Belgium

Age: 22. World ranking: 50

Goffin made his Grand Slam bow at last year's French Open, where he became the first "lucky loser" from qualifying to reach the last 16 of a Grand Slam tournament since 1995 before he lost to Roger Federer. His slight frame hides great stamina – he beat Radek Stepanek and Arnaud Clément in five sets in Paris before losing to Roger Federer – and he has an enterprising game. He did not win a match on the main tour until 2011 but beat Bernard Tomic and Jesse Levine at Wimbledon last year.

Grand Slam potential **