Boonen could now face criminal charges in Belgium
Belgian rider Tom Boonen has been banned from the Tour de France and could face a six-month ban after his second positive test for cocaine.
The 28-year-old, who first tested positive in May 2008, did so again in April and may face disciplinary action from the sport's ruling body.
His Quick Step have said they will contest the ban have said they plan to "contest by all legal means".
Boonen was expected to be a main rival to Briton Mark Cavendish in the race.
The International Cycling Union (UCI) had originally said it would not punish Boonen as the failed test was out of competition and not covered by its anti-doping rules.
But UCI chief Pat McQuaid is on record as saying Boonen will eventually face some kind of sanction even though he cannot face a traditional drugs ban.
It's not exactly an addiction. He's not a 'slave' to the substance but he uses it sporadically in specific circumstances
Quick Step chief Frank de Cock, speaking in May
"The sporting and economic damage for team and sponsors (which would arise from) the absence of Tom in the biggest race of the year are incalculable," said Quick Step manager Patrick Lefevere.
In the past, Lefevere has threatened to demand millions of euros in compensation if his rider was excluded.
However, Boonen, who won last month's Paris-Roubaix race, has severely tested the patience of his Quick-Step team with his latest indiscretion.
"Last year we went to the Tour de France organisers to plead Tom's case," said Quick Step chief Frank de Cock last month.
"There is no question of us doing that. We won't embarrass ourselves again.
"I put all my weight behind Tom last year, and told him I would forgive him, on the condition it did not happen again.
"Now, he's gone and done it again. He needs help. It would be a real pity for the sport of cycling to lose Boonen like this.
"It's not exactly an addiction. He's not a 'slave' to the substance but he uses it sporadically in specific circumstances."
Someone must teach me to understand what happens when I drink too much
A public prosecutor in Belgium said a search had been carried out at Boonen's home at the end of April in connection with a drugs investigation, although he did not reveal whether any illegal substances had been found.
Boonen told a Belgian television station: "For 364 days it goes perfectly, but the one day I drink too much I change.
"I will seek help. Someone must teach me to understand what happens when I drink too much.
"The night before the drug test, I went out. I stayed for a while and I drank. At some stage I must have taken something. Then I had a black-out.
"I think I have a problem. After spending three to four months working, when I go out I probably over-step the mark and I become someone else."
Boonen, who is a celebrity in his native Belgium, was barred from the Tour of Switzerland and Tour de France last year as a result of his first positive test for cocaine.
However, he did not face any sanctions from the International Cycling Union (UCI) because it does not hand down penalties for positive out-of-competition tests for the recreational substance.
In February this year, Boonen was given a suspended sentence by a Belgian court after he was found guilty of cocaine use.
His lawyer Luc Deleu said: "If it's proven that cocaine has been used, it would mean he didn't abide by the requirements set by the tribunal.
"In this case, his suspended conviction would be cancelled and there is a great risk he would need to go and face the tribunal."