Okon has reportedly waived his right for a second sample
A second Nigerian has failed a drugs test at the Commonwealth Games.
Samuel Okon, 24, who was sixth in the 110m hurdles won by Andy Turner, tested positive for the same drug as women's 100m winner Damola Osayemi.
According to Commonwealth Games Federation president Mike Fennell, Okon is waiving his right to the B sample test but this has yet to be confirmed.
Okon has been provisionally suspended and will attend a provisional hearing later today.
Okon and Osayemi both tested positive for methylhexaneamine, which is a stimulant that was added in 2009 to the World Anti-Doping Agency's list of banned drugs.
However, it was reclassified earlier this year and from the start of 2011 it can be used with a therapeutic use exception certificate.
CWF chief Fennell said: "We are concerned with the number of incidents that are coming up with the same substance.
"At this stage I cannot speak very definitively as to where it's coming from but it appears that it may be coming from the use of supplements.
"The supplements industry is by and large an unregulated industry worldwide and it is an industry that is a cause of great concern, not only for the fight against doping but also the protection of athletes.
If people think a substance is not on the banned list, they take it, and sometimes they are caught out when it is added to the list
BBC athletics commentator Steve Cram
"There are are all sort of claims as to what is in them and we have found that in many cases the claims are inaccurate. So many are misled into using these supplements."
Asked when the results for Okon's B sample test would be known, Fennell replied: "We have been informed that the athlete is waiving the right to the B sample (test) but this has yet to be confirmed.
"We will confirm this at his hearing this afternoon."
The Nigerian team have been informed and are also investigating.
"We have already had discussions with the leadership of the Nigerian team, who are themselves taking it very seriously. They are very concerned about it," Fennell told a news conference.
Recently, several Jamaican sprinters and 11 Indian athletes tested positive for methylhexaneamine.
The drug, which has some performance-enhancing qualities, is commonly found but often not labelled in supplements and products such as nasal decongestants.
As the BBC's Steve Cram notes, the drug can therefore be taken by accident: "If people think a substance is not on the banned list, they take it, and sometimes they are caught out when it is added to the list."
Four of the Jamaican sprinters were given three-month suspensions and talking about Osayemi's potential punishment, Cram said: "I would expect a ban of between three and six months, which is probably proportionate to the crime."