IAAF President Sebastian Coe admitted on Thursday that the doping test violations that US sprinter Christian Coleman is alleged to have committed are "not a good story" for the sport.
But Coe told AFP in an interview ahead of the Zurich Diamond League meeting the case showed that missing tests was taken seriously.
Coleman, this fastest man in the world this year over 100 metres, could face suspension after failing to make himself available for three drugs tests over the past 12 months.
It means Coleman would be forced to miss the World Championships in Doha later this year.
"It's not a good story but actually it does show the rest of the world we do take it seriously," Coe said.
"The whereabouts is a very serious element of the anti-doping discussion. I don't want to speculate.
"He's a phenomenal athlete and I will let this process run its course."
"I'm not a guy who takes any supplements at all, so I'm never concerned about taking drug tests, at any time."