Davis Cup organisers admit selling tickets for the revamped competition is proving a challenge with less than two weeks to go. Eighteen national teams will head to Madrid for the first edition of the week-long, World Cup-style event, which begins on 18 November. The new format, which has largely replaced the traditional home-and-away fixtures, was controversially approved at last year’s International Tennis Federation AGM despite vociferous opposition from a number of current and former players, officials and fans. The Barcelona footballer Gerard Pique’s Kosmos company is the financial muscle behind the event having pledged to invest £2.3bn over 25 years, but efforts to recoup some of that money through strong ticket sales are proving problematic. A spokeswoman for Kosmos said: “We are happy with ticket sales for the afternoon sessions and from Friday until Sunday (quarter-finals, semi-finals and final) but it’s much more difficult to sell tickets for morning sessions, as happens in all tournaments.” The disappointing sales come despite countries naming strong teams, which was the main objective of the change of format. Six of the men’s world top 10 will be in Madrid, including Rafael Nadal and Novak Djokovic, with Germany’s Alexander Zverev the only eligible player to…