The world No. 2 was expected to represent Spain against the United States next week in the quarterfinals, but he was left off the official roster released on Tuesday by the International Tennis Federation.
Nadal missed four months last year because of an injury to his right foot. The problem resurfaced this month in Dubai, and he didn't want to aggravate the injury on hardcourts before the start of the European claycourt season.
The two-time French Open champion also missed the first-round tie against Switzerland because of an injury. Spain still beat the Swiss team, minus top-ranked Roger Federer, 3-2.
The quarterfinals are scheduled for April 6-8.
In the other three quarterfinals, it's: Russia vs. France; Belgium vs. Germany; and Sweden vs. Argentina.
Instead of Nadal, Spain will have Tommy Robredo, David Ferrer, Fernando Verdasco and Feliciano Lopez when it travels to Winston-Salem, North Carolina.
Andy Roddick, who will play singles for the United States, said he was disappointed that Nadal will be absent and surprised by the decision.
"Personally, I don't know if you can play Davis Cup at your convenience," Roddick said. "I think it's a yearlong commitment."
With Roddick were No. 8 James Blake, and the top-ranked doubles team of Mike and Bob Bryan.
Fourth-ranked Nikolay Davydenko will lead Russia against France on indoor clay in Moscow. He will be joined by Marat Safin, Mikhail Youzhny and Igor Andreev.
Richard Gasquet, Paul-Henri Mathieu, Michael Llodra and Arnaud Clement will represent France.
On indoor clay in Ostend, Belgium, Olivier Rochus, Kristof Vliegen, Dick Norman and Christophe Rochus will play for the hosts against Tommy Haas, Florian Mayer, Alexander Waske and Michael Kohlmann.
Sweden, which will host Argentina on indoor carpet in Goteborg, will have Robin Soderling, Jonas Bjorkman, Thomas Johansson and Robert Lindstedt against Argentina's David Nalbandian, Guillermo Canas, Juan-Martin Del Potro and Sebastian Prieto.