Eighteeen nations will gather in Madrid's La Caja Mágica on Monday as the men's tennis season culminates with a revamped Davis Cup format dreamt up by a man who earns his living playing soccer for Barcelona.

The new Davis Cup format

The week-long football World Cup-style Davis Cup Finals will be the biggest shake-up the 119-year-old team event has ever had and is being bankrolled by Barça defender Gerard Piqué's investment firm Kosmos to the tune of 2.7 billion euros over 25 years.

It has not been smooth sailing for the International Tennis Federation (ITF) since it announced the radical revamp with some accusing the organisation of selling the soul of a competition loved by tennis diehards, but which had slowly lost its lustre. There is also the small matter of the ATP Cup - seen as a rival competition - launching in January. As for any large sporting event the key ingredient will be the quality of the entertainment and the atmosphere. Nineteen-time Grand Slam champion Rafael Nadal will lead the Spanish team, while Novak Djokovic will play for Serbia, Andy Murray for Britain and Nick Kyrgios will surely spice things up as he turns out for Davis Cup heavyweights Australia. But there will be notable absentees. Roger Federer's Switzerland failed to qualify, world number five Dominic Thiem's Austria also missed out while Germany will be without Alexander Zverev, who has shunned the event. Fast-rising Russian Daniil Medvedev withdrew this week to recover after a long season while other big names such as Canada's Milos Raonic are injured.

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Eighteen nations in six groups fo three

The format will involve the 18 nations, which include two wildcards, split into six groups of three with the winners and best two runners-up moving on to the knockout phase. Group ties will involve two singles and a doubles with rubbers played over best of three sets tiebreak sets. The final will be contested next Sunday. As well as the main arena at La Caja Mágica (The Magic Box), matches will also be played on two smaller courts to enable the jam-packed schedule to be completed in a week.

Criticism of the event

Critics of the new venture cited the loss of the uniquely partisan Davis Cup atmospheres. While Spain will be vocally backed and Britain has sold 1,000 tickets, the prospect of matches taking place in front of banks of empty seats will worry organisers. Murray, who famously won the Davis Cup for Britain in Ghent in 2015, roared on by deafening crowds, said while he is intrigued by the new format, he is concerned that the Magic Box might be lacking the magic created by the fans: "I'm going to miss that but I love being around the team and I'm excited to see what the new format looks like and I hope the atmosphere is brilliant," he said. "That's my one concern."

 "Ready for something unexpected" - Nadal

Croatia will arrive as defending champions having won the last traditional final last year against France in Lille and will face a tough task in Group B where they take on Spain and Russia without top player Marin Cilic. Nadal, despite some abdominal issues, is expected to line up for Spain, although whether or not he would last a potential five singles matches in six days is doubtful. The 33-year-old said fans should expect the unexpected. "Of course is something special, something new, and when it's something new, you need to be ready for something unexpected,'"he said. "Let's see how the things work."