Nuria Llagostera Vives has been banned from playing tennis for two years under anti-doping rules.
The Spanish veteran, 33, tested positive for d-methamphetamine at the Bank of the West Classic in Stanford this summer.
A statement from the International Tennis Federation read: "An independent hearing was held, in which Ms Llagostera Vives was not able to demonstrate how the d-amphetamine entered her system.
"She was, therefore, unable to satisfy the preconditions for mitigation."
Vives reached career-high singles ranking of 35 in 2005 but has played only doubles in the last two years.