A second doping case in two days, again involving a Nigerian runner, has cropped up at the Commonwealth Games.

Commonwealth Games Federation President Mike Fennel says Samuel Okon, who was sixth in the 110-meter hurdles final last Friday, tested positive for the banned stimulant Methylexanemine.

It was the same substance that was found in a sample from women's 100 champion Osayomi Oludamola last week.

Fennel says "we ourselves are concerned with the number of incidents that have cropped up with this substance."

The games in New Delhi have been plagued by problems with ticketing, near-empty stadiums, construction delays and filthy conditions in the athletes' village before the games began, but doping is out of their control.