FIFA overturned a provisional suspension handed down to an unnamed Bulgarian international for a failed drugs test on Thursday, just hours after the sanction was imposed.
World football's governing body had initally banned the player after he returned a test with "an adverse analytical finding" following his country's 2014 World Cup qualifier in Malta on September 10.
But the suspension has since been wiped out after medical advice from FIFA's medical experts.
"The chairman of the FIFA Disciplinary Committee has revoked his decision to suspend a Bulgarian international footballer for a period of 30 days," said FIFA in a statement.
"The decision was taken following clarification by medical bodies, on the basis of which it appears that there is no circumstantial evidence that anti-doping rules have been violated."