That positive test could see him face criminal charges by public prosecutors.
According to Velonews.com:
"The 28-year-old escaped a sports sanction because the test was not held under the auspices of a sport body, however his team, Quick Step, pulled him off their Tour de France squad after race organizers expressed concerns.
Now the Flemish cycling star, who has recently returned to live in Belgium from Monaco, has been told to expect by January 6 to learn whether he will face charges or not.
According to sources at the prosecutors' office Boonen would risk between three months and five years in prison and a fine of between 1,000 and 100,000 euros.
Boonen admitted to cocaine use in June and tried to win back fans with a public apology."