The players and team captain are upset that the Spanish tennis federation appears to be ready to overlook home-court advantage in favor of sponsorship money.
Madrid is one of four cities vying to host the Sept. 19-21 best-of-five series at the Las Ventas bullring. Benidorm, Tenerife and Gijon are also trying to win the right to host the event.
The Spanish players are worried that Madrid's 1,800-foot altitude - making it the highest capital city in Europe - will take away its precious clay-court advantage against the defending champions.
They believe that Andy Roddick's booming serve and the hard-hitting doubles pair of Bob and Mike Bryan will be equal to the hosts despite playing on their least favorite surface.
Madrid's sudden place as the front-runner comes about three months after the city's tourist office signed up as a key sponsor with the Davis Cup through 2010.
"What I know is that as of today it hasn't been decided where the Davis Cup semifinal will be staged,'' federation sporting director Javier Duarte said. "That which has the best specifics will take the semifinal.''
Marca newspaper reported Tuesday that Spain captain Emilio Sanchez Vicario had sent the federation his notice of resignation because his objections to playing in Madrid had fallen on deaf ears, with Madrid already believed to be a lock.
Federation president Pedro Munoz dismissed the reports that Sanchez Vicario had resigned on Tuesday, while Duarte denied that a players' rebellion was brewing.
"You have to respect that, every player and every captain has his preferences,'' Duarte said. "I was once captain and opinion is important. You have to listen to all sides and undertake a valuation of all information.''
Juan Carlos Ferrero, who was part of the Spanish team that beat the Americans in Seville nearly four years ago for the title, said problems were brewing.
"We players want this to be solved in the best way possible, but if it has to be done the worse way, then it will be,'' the former top-ranked player said from the Rome Masters.
The federation will make its decision Friday, but then has several days to relay its decision to the International Tennis Federation, which is expected to announce the host city by May 13.
Benidorm's Parque Tematico Tierra Mitica, the Parque Hermanos Castro in Gijon and the Estadio Olimpico Arturo Dominguez in Tenerife are the other venues.
The slowest of all playing surfaces, clay is a more physical surface with its lengthier baseline rallies due to balls taking on heavier topspin.
Three-time French Open champion Rafael Nadal will play for Spain if is healthy. He has won 103 of his last 104 matches on clay.
Roddick lost both of his singles matches against Spain at the Stadio Olimpico in 2004 in front of a record crown of 27,200.
"I hadn't really been following that, to be honest,'' Roddick said from Rome on Tuesday. "There's a lot of big events between now and then ... so it's not something I think about daily.''
Roddick, who trails only John McEnroe and Andre Agassi in Davis Cup wins for the United States, said he would be happy with whatever city the federation choses.
"I'm sure wherever it is it's going to be fine. It's always nice when there's interest,'' the sixth-ranked American said. "Any time there's that kind of attention drawn to tennis and that excitement, it's not going to be a bad thing.''
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AP Sports Writer Andrew Dampf in Rome contributed to this story.
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