Botswana's former world 400 metres champion Amantle Montsho has failed a drugs test, the Commonwealth Games Federation has announced.
Montsho, who won the world title in 2011 before finishing second behind Christine Ohuruogu last year, tested positive for the banned stimulant methylhexaneamine after the 400m final in Glasgow.
The 31-year-old, who could only finish fourth at Hampden Park last Tuesday, will have her B sample tested on Monday.
Montsho, who came into the Games as the defending champion, has been provisionally suspended.
A statement from the CGF read: "In accordance with the CGF anti-doping standard for the XX 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.
"Ms Montsho attended the provisional hearing of the federation court, presided by CGF vice-president Bruce Robertson, which ruled that the provisional suspension of the athlete will continue.
"Upon receipt of the analysis of the athlete's B sample, the court will reconvene to consider the matter further."
Montsho is the most high profile athlete to have failed a drugs test at the Games, which have also seen 16-year-old Nigerian weightlifter Chika Amalaha stripped of her gold medal.
Montsho finished fourth at London 2012 and was favourite for the world title in Moscow last summer only to be beaten to the gold by four thousandths of a second by Ohuruogu.
She had been expected to get on the podium in Glasgow, but was edged out by the Jamaican trio of Stephenie McPherson, the champion, Novlene Williams-Mills and Christine Day.
Her positive test follows those returned by Welsh pair Gareth Warburton and Rhys Williams ahead of the Games.
Methylhexaneamine was only added to the World Anti-Doping Agency banned list in 2010.
It is the same substance that Yohan Blake, the Jamaican sprinter, tested positive for the year before. He received a three-month ban even though it was not then on the banned list.
The news about Montsho both surprised and disappointed 400m rival Ohuruogu.
"I heard about it just before we came out," the English sprinter said after winning Commonwealth bronze in the 4x400m relay.
"I didn't really want to think too much about it.
"My initial reaction was desperate disappointment, but I think before I say too much about it I need to find out exactly what happened."