(CNN) -- The Commonwealth Games was hit by a fresh doping scandal Saturday after former world 400m champion Amantle Montsho of Botswana failed a drugs test.
Montsho, who was the defending her Commonwealth title in Glasgow over her specialist distance, tested positive after Tuesday's final for the banned stimulant methylhexaneamine.
The 31-year-old had finished a disappointing fourth at Hampden Park behind a Jamaican clean sweep led by Stephanie McPherson.
A statement from the Commonwealth Games Federation (CGF) said: "In accordance with the CGF anti-doping standard for the Commonwealth Games, the CGF federation court conducted a provisional hearing this afternoon to consider an adverse analytical finding submitted by Amantle Montsho of Botswana, after the women's 400 metres final on July 29.
"The athlete's A sample was found to contain methylhexaneamine, prohibited as a stimulant under class s6 of WADA's Prohibited List.
"Ms Montsho was notified of her A sample result and has asked for her B sample to be tested, which will take place at the accredited laboratory in London on Monday August 4."
Montsho was feted in Botswana after claiming the Commonwealth Games crown in Delhi in 2010 and she built on that success to take the world title in 2011.
She finished second to Britain's Christine Ohuruogu in her defense of that title in Berlin last year and came into the Glasgow Games as one of the favorites.
Montsho is by far the most high profile athlete to have failed a drugs test at the Games.
Earlier this week, 16-year-old Nigerian weightlifter Chika Amalaha was stripped of her gold medal after giving positive tests for prohibited diuretics and masking agents.
Welsh track and field competitors Rhys Williams and Gareth Warburton were withdrawn from their respective competitions before the start of the Games after failing doping controls.
The track and field action at the Games concludes later Saturday, with six-time Olympic champion Usain Bolt running the anchor leg for Jamaica in the 4x100m relay.