Former world champion Tom Boonen faces an anxious wait to see if he can start the Tour de France on Saturday after a judge said she could not rule in his case against the organisers who say he is unwelcome.

Boonen launched a court case against Amaury Sport Organisation when it said he could not race in this year's Tour after testing positive for cocaine.

"The judge has informed us the French court does not have the legal basis to rule in this case," the Belgian rider's lawyer Jean-Louis Dupont told Reuters yesterday.

"The judge said the case must be heard by the French Court of Arbitration for Sport and our client has instructed us to start an appeal case there. We expect a ruling in the coming days, certainly before the Tour starts."

Boonen's Quick Step team said in a statement yesterday they had decided to lodge an arbitration request to permit Boonen to start the race. They also cancelled his news conference planned for later on in the day.

The 28-year-old cyclist, who won the World Championship in 2005, failed an out-of-competition test for cocaine in April, his second offence in 12 months after he also tested positive for the same substance last year.

Boonen missed last year's Tour following his first failed test for cocaine. He was banned by Quick Step last month after it was announced he had failed the test, before returning to racing this month.

Failing an out-of-competition check for cocaine is not technically considered a positive doping test since the use of the substance is not banned between races.

Earlier this month, the International Cycling Union said it would not open disciplinary proceedings against Boonen after threatening him with a six-month ban for spoiling the sport's image.