Jeremy Mayfield has been suspended indefinitely from NASCAR after failing a random drug test at Richmond International Raceway.
The 39-year-old, who drives for his own team in the Sprint Cup Series this season, was found to be in violation of NASCAR's substance abuse policy, as results of a test taken last week revealed.
No details have been disclosed of what substance was found on Mayfield, but a NASCAR spokesman confirmed that it was not alcohol-related.
Mayfield said in a statement that a mix of medicines had probably caused the results of the test to be positive.
"As both a team owner and a driver in the NASCAR Sprint Cup Series, I have immense respect for the enforcement policies NASCAR has in place," said Mayfield. "In my case, I believe that the combination of a prescribed medicine and an over the counter medicine reacted together and resulted in a positive drug test.
"My Doctor and I are working with both [NASCAR consultant] Dr [David] Black and NASCAR to resolve this matter.
"Mayfield Motorsports remains committed to the NASCAR Sprint Cup Series and the organisation will announce an interim owner and a temporary replacement driver early next week.
"Those roles will commence immediately beginning with next week's Sprint Open and continuing through Charlotte and beyond."
The five-time Cup race-winner had been one of two drivers who failed to qualify for Saturday's race at Darlington Raceway, the sixth time this year he had been unable to make the field.
Back in February Paul Chodora, a crew member on Mayfield's team, had been suspended for the same reasons as Mayfield is being now punished.
Before the season started the sanctioning body announced the enforcement of a new substance abuse policy, which includes random drug tests not only for drivers but also for crew members.
Two crew members from other teams, one from the Sprint Cup and another from the Nationwide Series were also suspended on Saturday after testing positive as well.