Alex Bogomolov Jr. will play for Russia instead of the United States after the International Tennis Federation approved the switch on Thursday.
Bogomolov, born in Moscow, has represented the US since turning professional in 2002 but has never played at senior level in the Davis Cup.
He is listed by the ATP as Russia's top-ranked player at No. 34, one spot ahead of Nikolay Davydenko. He was the fourth-ranked American.
"The USTA has been a longtime supporter of Alex Bogomolov through direct financial grants as well as coaching and training. We are disappointed with the ruling of the ITF's Davis Cup Committee, but respect its decision," the USTA said in a statement emailed to The Associated Press.
"We understand Alex's decision and hope he recognizes the amount of resources and commitment we have provided to him over the years."
A Davis Cup Committee decided Bogomolov's case met 2012 regulations which allow national federations three months instead of six before a tie to submit a request for a player of dual nationality to represent the country.
Russia submitted a request in October, meaning Bogomolov is eligible to play in the first round of the Davis Cup against Austria from Feb. 10-12.
US Davis Cup captain Jim Courier noted Bogolomov's ascent in the rankings, and that he's "really a factor" on the tour. Still, Courier said Bogolomov wasn't in his plans.
"He hasn't factored into my thoughts for what our team is and will be," Courier said during a US Tennis Association conference call. "I don't really see a scenario where he would be playing for the United States. So I wish him well."
ATP players recently voted Bogomolov as the most improved tour player after he rose from No. 166 at the end of 2010 to a career-high No. 33 in November.
His father, Alex Bogomolov, is a renowned tennis coach in the former Soviet Union, who coached Yevgeny Kafelnikov and Andrei Medvedev among others. Bogomolov Jr. moved to Mexico with his family when he was 9, and in 1992 on to Florida, where he is still based.