It is still early in the season, of course, but a game that will be watched by millions worldwide could have a huge bearing on a title battle that was only ever going to involve two teams.

Unbeaten in all competitions, Real Madrid lead La Liga having won 10 and drawn two but Barcelona remain just a point behind. The game will match up not only two of the game's most influential coaches, but also the world's two best players.

Former World Player of the Year Ronaldo has put together an incredible run of goals for Real since the start of October, scoring 17 in 12 matches. Current World Player Lionel Messi is also on a hot streak. Barca's Argentina forward scored his sixth goal of this season's Champions League in Athens and has 13 league goals, one short of Ronaldo.

Some of the key head-to-heads in the "Clasico" between La Liga giants Barcelona and Real Madrid at the Nou Camp on Monday night.

Photographs: Reuters

World player of the year Lionel Messi, 23, and former holder Cristiano Ronaldo, 25, are playing some of the best football of their careers.

The Argentina forward scored a hat-trick against Almeria last weekend to take his league tally to 13 but Portuguese Ronaldo matched him with a treble against Athletic Bilbao to top the scoring charts on 14.

Both players have the freedom to roam off the flanks and are often most dangerous driving down the centre, dribbling past opponents and playing one-twos.

Their styles are very different.

Messi plays with schoolboy enthusiasm, making darting runs and exchanging quick passes with team mates. Ronaldo is more of a showman, making muscular charges down the pitch, and his powerful, swerving freekicks are a threat from any range.

Spain's David Villa, 28, and Argentina's Gonzalo Higuain, 22, are the leaders of the line for their teams but not the top scorers.

Villa arrived from Valencia for 40 million euros ($53.3 million) in the close season and although goals have been relatively hard to come by he has slotted in quickly with his Spain international team mates. He has scored six and set up four in the league so far.

Higuain, who has bagged seven league goals and had three assists, is steadily shaking off the tag of being a player who fails to score in big games.

The Spain midfielders, who operate in slightly different roles, are considered irreplaceable.

Playmaker Xavi, 30, is the heart of Barca and Spain's possession-based football and covers a huge amount of ground in a match, linking up play and creating chances. He has been used sparingly this season having struggled with sore Achilles' tendons.

Xabi Alonso, 29, is more defensive, playing alongside Sami Khedira in a holding role at Real, but his passes, especially balls from deep in his own half to launch counter-attacks, are a major feature of his side's play.

In the past, the delicate skills of the likes of Andres Iniesta, 26, and Mesut Ozil, 22, would have been considered too lightweight to survive in the midfield battlegrounds of top-flight football but they now seem to represent the future. Gifted playmakers who open up spaces by running at defenders, they set up scoring chances and have an eye for goal.

They are timid characters off the pitch but seem to engender a special kind of respect from the fans. Iniesta's World Cup-winning goal for Spain earns him applause from rival fans, while Germany's Ozil has regularly received standing ovations from Madrid fans when substituted. Just do not expect to see either of them putting in crunching tackles.

Victor Valdes, 28, is one of the best goalkeepers in the world. He has won two European Cups, four La Liga titles and been crowned La Liga goalkeeper of the year three times for conceding the fewest goals.

However, there are few who would question Iker Casillas's right to the title of Spain's number one.

Valdes is an imposing presence who acts as the starting point for much of Barca's possession play. His distribution from the back is one of the aspects of the game they spend a lot of time working on in training.

Real's Casillas, 29, has earned the nickname "Saint Iker" and is an outstanding shot stopper.

The shaggy-haired Carles Puyol, 32, has marshalled Barcelona's and Spain's central defence for much of the last decade and in Gerard Pique has found a perfect partner.

While Puyol shouts out instructions and tears around the pitch making last-ditch tackles, Pique provides a more calming presence and a more creative outlet from the back.

Portugal's Ricardo Carvalho was lured from Chelsea by his former boss Jose Mourinho and immediately became the boss of Real's backline alongside compatriot Pepe.

His reading of the game is excellent and his arrival has led to a tightening up of their defence. They have only conceded six times in 12 league outings.