Australia captain Lleyton Hewitt is standing by his criticism of the new-look Davis Cup and maintains the format should never have been changed.

The 18-team, world cup-style event begins in Madrid on Monday with the winners from each of the six groups progressing to the quarter-finals on Thursday along with the two best runners-up.

Hewitt, who played in 43 ties during his career, has been one of the most vocal opponents of the changes, which see matches now played over three sets rather than five.

"I still feel the same way," said Hewitt.

"In terms of the Davis Cup and how we all knew it ... two of the biggest differences and what the competition was all about was home and away ties and matches played over five sets.

"You couldn't do that in any kind of form in our great game and if you look at the pinnacle of our game, which are the grand slams, they are played over five sets.

Lleyton Hewitt's still unhappy with the new-look Davis Cup but says the team will give it their all. Credit: AAP

"But this is a new format and as I said at the start of the year, our boys get to wear the green and gold and play for their country.

"It doesn't matter if we are playing marbles out there, we're going to lay everything on the line and do what we can to represent our country and make everyone back home proud.

"In terms of that, nothing changes and we have to go out there and do our best."

Barcelona and Spain footballer Gerard Pique's Kosmos company are behind the new event after acquiring the rights from the International Tennis Federation for the next 25 years for $A4.4 billion.

Last week Roger Federer, who is not in action after Switzerland failed to qualify, said the tournament was in danger of becoming the Gerard Pique Cup.

World No.7 Alexander Zverev has also been highly critical of it and refused to take his place in the Germany team.

"I don't think the format is Davis Cup anymore," said Zverev.

"I think Davis Cup is the most historic event that we have in tennis, which is over 100 years old, and Davis Cup is the home-and-away ties.

"That's Davis Cup for me, and not playing it at one venue for one week and deciding it all."

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The tournament has been heavily marketed in Madrid, with the names of local train stations en route to the Caja Magica venue changed to those of the players who are competing.

However, ticket sales have initially been slow despite 10 of the world's top 15 players taking part, including world No.1 Rafael Nadal and No.2 Novak Djokovic.

Australia open their campaign against Colombia at 0400 AEDT on Wednesday and face Belgium on Thursday at the same time.