Querrey was chosen ahead of Blake for the best-of-five series against Spain on outdoor clay Sept. 19-21 in Madrid. It was unclear why the 11th-ranked Blake was dropped.
Andy Roddick and doubles specialists Bob and Mike Bryan round out the U.S. team selected by captain Patrick McEnroe.
Last year, Blake teamed with Roddick and the Bryans to lead the Americans their record 32nd Davis Cup title.
Spain captain Emilio Sanchez Vicario selected top-ranked Rafael Nadal, David Ferrer, Fernando Verdasco and Feliciano Lopez.
Querrey was listed on the official nomination released by the International Tennis Federation, but it noted it was still awaiting confirmation on his eligibility. Querrey, ranked No. 40, has never played in the Davis Cup.
Last week, McEnroe said Blake would be on the team with Roddick and the Bryan brothers for a record 11th straight time.
Nicolas Almagro was listed as a reserve for Spain, while 16th-ranked Tommy Robredo was left off the team.
Nadal, who lost to Andy Murray in the semifinals of the U.S. Open on Sunday, may get a few days rest before joining the team.
"He lost a match, but the tiredness and stress are within the usual limits,'' Sanchez Vicario said of Nadal, who may not attend practice Saturday. "He is very enthusiastic about this tie.''
Argentina will host Russia on outdoor clay in Buenos Aires in the other semifinal series.
Sixth-ranked Nikolay Davydenko of Russia will play alongside Igor Andreev, Dmitry Tursunov and Igor Kunitsyn. Marat Safin was again passed over.
Argentina will counter with David Nalbandian, Juan Martin Del Potro, Agustin Calleri and Guillermo Canas.
In the World Group playoffs, U.S. Open champion Roger Federer will lead Switzerland, and Australian Open champion Novak Djokovic will guide Serbia.
Federer rebounded from losses in the French Open and Wimbledon finals to win his 13th Grand Slam title on Monday at the U.S. Open - one shy of Pete Sampras' all-time record.
Federer will play against visiting Belgium on indoor hardcourts in Lausanne, and Murray will help Britain against Austria on the grass at Wimbledon.
Murray will team with brother Jamie Murray, Alex Bogdanovic and Ross Hutchins against Austria's Jurgen Melzer, Alexander Peya, Martin Fischer and Julian Knowle.
Djokovic, who lost to Federer in the U.S. Open semifinals, will team with Janko Tipsarevic, Viktor Troicki and Nenad Zimonjic on outdoor hardcourts against Slovakia.
The Davis Cup final will be played Nov. 21-23.
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