Commonwealth 400m champion Christine Ohuruogu has been provisionally suspended by UK Athletics after missing three out-of-competition drugs tests.
Ohuruogu was a strong medal prospect in Sweden
The 22-year-old was one of Britain's best medal hopes at this week's European Championships in Gothenburg but has been withdrawn from the team.
UKA said Ohuruogu had missed three tests in 18 months.
In a statement, the Londoner claimed that changes in her training schedule had caused the problem.
Ohurougu admitted it was her responsibility as an elite athlete to make her programme known to UKA at all times.
She said: "Due to changes in my training schedule, I was unable to fulfil this obligation on three occasions, hence, my current suspension.
"I want to apologise for the distress and concern I have caused the people closest to me and UK Athletics, who, at the end of the day, we all understand are trying to uphold an incredibly hard rule.
"My duty is to always do my best and I am massively disappointed that this suspension means I cannot represent my country at the European Championships."
UKA said the provisional suspension should be viewed as a case to answer rather than an indication of guilt.
But performance director Dave Collins said: "This is a sign of the stringent testing procedures which UKA are totally committed to."
UKA said its anti-doping co-ordinator has found that sufficient evidence of a rule violation to invoke the governing body's disciplinary procedure.
A statement said: "If an athlete is evaluated as having missed three out-of-competition tests in a period of 18 months from the date of the first missed test, an anti-doping rule violation has been committed.
"In this case, the first out-of-competition missed test was on 12 October 2005.
"The case will now be put to an independent disciplinary committee to decide if an anti-doping violation has been committed.
"The panel will be convened as soon as is practical."
Earlier this year, Ohuruogu upset world and Olympic champion Tonique Williams-Darling in the Commonwealth final by winning gold in a personal best time of 50.28 seconds.
She has competed over the distance only twice since that victory in Melbourne because of an Achilles injury.