Howard Jacobs said Taurasi's "A" sample came back positive from a Turkish lab last week and she was provisionally suspended by the Turkish league she's playing in. She has already missed three games with her team, Fenerbahce.
Jacobs said the substance "was not a steroid or recreational drug," and that Taurasi has asked that her "B" sample be tested.
"We're taking it one step at a time," Jacobs said. "I'd rather not say what it is at this stage, they've only tested the 'A' sample. Somehow it leaked over in Turkey. We're waiting for the 'B' sample to be tested. We've had some difficulty with getting a date so far, mostly because of the holidays. We're hoping to get it as soon as we can."
Taurasi's positive test came to light two days after her former Huskies won their 89th straight game, surpassing the UCLA's men's team winning streak set from 1971-74. Taurasi helped lead UConn to three straight national championships as well as 70 consecutive victories from 2001-03. She was the AP Player of the Year in 2003.
A call to UConn coach Geno Auriemma was not immediately returned.
"While she is fully cooperating with authorities, there are serious doubts about the accuracy of the test results," Jacobs said in a statement to the AP. "We are confident that Diana will be fully vindicated once all the evidence is reviewed. She regrets that someone has violated the confidentiality rules of this process, and will make no further statement at this time."
WNBA spokesman Ron Howard said the league had no comment. "In the 10 years of competition at the collegiate, professional and Olympic level," Jacobs said, "Diana Taurasi has never taken, been suspected of using, or tested positive for any performance enhancing substance."
He said he said he didn't know what the length of the suspension would be, nor was he familiar with the details of the Turkish league's anti-doping code. He also said said it was too early to know how this might affect Taurasi's eligibility for the London 2012 Games. The International Olympic Committee bars any athlete given a doping penalty of six months or more from competing in the next games.
Taurasi, who has won two Olympic gold medals, helped guide the U.S. national women's basketball team to the world championship in early October. She led the WNBA in scoring for a league-record fourth straight year, averaging 22.6 points per game. The five-time All-Star and two-time WNBA champion signed a multiyear contract extension with the Phoenix Mercury in August.
Reached at the Miami Heat-Phoenix Suns game, Rick Weltz, president of the Suns and Mercury, said the team had no comment.
Taurasi served one day in jail and was suspended by the team for two games in 2009 after pleading guilty to a DUI charge.
She played in Russia for four years for powerhouse Spartak before joining Fenerbache in the Turkish League this season. That league also features WNBA stars Sylvia Fowles, Penny Taylor and Seimone Augustus.