Commonwealth Games women's 100m gold medal winner Damola Osayemi has failed a drugs test.
She has been provisionally suspended until the result of her B sample is received on Wednesday.
The Nigerian, 24, was named champion on Thursday after Australia's Sally Pearson was controversially disqualified for a false start.
England's Katherine Endacott finished fourth but could now be handed silver if the decision is upheld.
The sprinter showed traces of a banned stimulant called methylhexaneamine, which has only recently been added to the World Anti-Doping Agency's prohibited list.
Games chief confirms failed drugs test
Osayemi requested the testing of her B sample after which the Commonwealth Games Federation released a statement.
"The provisional hearing ruled that the provisional suspension of the athlete will continue until the result of the B sample is received," the statement read.
"That B sample result is expected within 48 hours from the time of the request; so further details are not expected until Wednesday morning [Delhi time]."
If the B sample proves positive, Natasha Mayers of St Vincent and the Grenadines would be handed the gold, which would be the country's second ever Commonwealth gold medal.
Endacott, who finished fourth in the race behind Pearson and the Nigerian but was later awarded the bronze medal, would be elevated to a silver.
Osayemi could either be handed a warning or could serve up to a two-year ban.
At his daily news conference, Fennell said: "Any positive test - whether in a high-profile event or not - is something that is very much regretted because we all strive for a clean Games, clean sport and clean competition.
"One doesn't know what sort of damage will accrue but we want to let everyone know we are very vigilant and the testing is of the highest standard."
Explaining why the news had been confirmed now, rather than waiting for the B sample, Fennell added: "We recognise there is difficulty in maintaining complete secrecy during the process."
Lalit Bhanot, the organising committee's general secretary, said: "We want a dope-free Games. If somebody is caught, action will be taken. At the same time it is a message that no-one can escape."
Methylhexaneamine is the same drug several Indian athletes, including weightlifter Sanamacha Chanu and swimmers Richa Mishra and Jyotsana Pansare, were found to have used in September.
Wada subsequently moved it to the non-specified list, meaning it can be used with a therapeutic use exception certificate.
The Indians subsequently appealed against their bans but there has been no verdict yet.
According to companies that market products that contain methylhexaneamine, the drug stimulates the central nervous system.
It gives the body an energy boost by increasing the body's metabolic rate.
Nigeria's Athletics Federation president, Solomon Ogba, has reportedly claimed Osayemi was given prescription medicine to fight a nagging toothache.
"She took medication for her toothache and we strongly suspect that it was that, which led to her failed drug test," he stated.
The BBC's Steve Cram was not surprised to hear that this particular drug was involved.
"The stimulant she has been caught for has caused problems for athletes over the past year," he said.
"It's a commonly used stimulant as a nasal decongestant and, leading into the Games, there were 11 Indians from different sports who had tested positive for methylhexaneamine, so it's pretty prevalent."