Noah Lyles said he was "shocked" by fellow American sprinter Christian Coleman's three missed drugs test which have left the world championship 100-metre favourite facing a possible suspension.
The 22-year-old Lyles, who snatched headlines by running a world-leading 19.50 seconds in the 200 metres at the Lausanne Diamond League event last month, said it was "none of his business" when asked whether or not he thinks Coleman is a clean athlete.
Britain's Daily Mail and The Times newspapers reported that Coleman, a late withdrawal from last Sunday's Diamond League meeting in Birmingham, is challenging one of the three alleged "whereabouts" failures in the past 12 months.
Athletes who fail to make themselves available for three drug tests are treated the same as athletes who fail a drug test and face an automatic ban.
"I've been shocked. You don't expect anybody to be missing three," said Lyles ahead of Saturday's Diamond League meeting in Paris.
"You don't know why. It could be a multitude of things so I don't know."
Any suspension of Coleman would represent another bodyblow against athletics just as the sport attempts to move on from the Russian doping scandal.
Coleman, the world record holder over 60m and world indoor 60m champion, has emerged as the most likely successor to Usain Bolt following the Jamaican sprint king's retirement in 2017.
Lyles insisted he would focus on his own racing.
"You gotta know what you're doing is clean," he said. "I know what I'm doing is clean and keep hoping that everybody is doing the same thing."
Coleman, 23, took 100m silver at the 2017 worlds in London behind Justin Gatlin, but his participation in this year's championships in Doha, which start on September 28, is now in doubt.