American Varvara Lepchenko has been provisionally suspended for an anti-doping rule violation, the International Tennis Federation has confirmed.
The 35-year-old returned a positive test which contained metabolites of adrafinil and/or modafinil at the Hungarian Grand Prix in July.
Both substances are banned by the World Anti-Doping Agency, the ITF said.
Lepchenko is 124th in the WTA world rankings.
A pre-charge notice was issued to Lepchenko, who formerly represented Uzbekistan, on 9 August and her provisional suspension came into effect on Thursday.
The ITF added: "Lepchenko had (and retains) the right to apply to the chair of the independent tribunal convened to hear her case why the provisional suspension should not be imposed (or should be vacated), but has not exercised that right."
Lepchenko last competed at the Thoreau Tennis Open in Concord, Massachusetts, at the start of August and was beaten by Russian Vera Zvonareva in the last 16.