Freitag was stopped by Tshwane police on Friday morning after he allegedly ran a red traffic light in Bronkhorstspruit.
The drug was then allegedly found in his pocket.
Police spokesperson Captain Sarah Mcira said Freitag would remain in custody through the weekend.
He is one of only eight athletes to win world championships at the youth, junior, and senior level of an athletic event.
Freitag won the gold medal at the World Athletics Championships in Paris, France in 2003.
In 2006, Freitag, along with his gym partner Zeegfriedt Veenemans were arrested after a fight broke out between them and a 17-year-old pupil.
A charge of assault against them was dropped after they attended a diversion programme.