Three-time Tour de France champion Alberto Contador says he is mentally tough enough to defend his title under the intense pressure and scrutiny of an ongoing doping case.

The Spaniard begins his quest for a fourth win on Saturday, having been cleared by the Spanish cycling federation after testing positive for the banned anabolic agent clenbuterol in last year's race.

The International Cycling Union and World Anti-Doping Agency have appealed the ruling to the Court of Arbitration for Sport. Should they win, Contador faces the strange prospect of losing his 2010 title days after possibly winning another one.

"The pressure is not only on the road but also outside of it, there is more and more and I am conscious of that," Contador said through a translator on Thursday. "To focus on the race is something I've been used to doing now for many years. I have no problem with that."

The 28-year-old Contador is not easily fazed, whatever the scenario, and has a ruthless streak essential to champions.

He rode on the same team as Lance Armstrong on the 2009 Tour, withstanding intense pressures within that team to beat the seven-time champion and clinch his second Tour win.

Last year, Contador was locked in an intriguing duel with Luxembourg rider Andy Schleck, a race that went all the way through the mountains and turned in Contador's favour after some thrilling tussles in the climbs.

Contador chose not to wait when Schleck had a mechanical problem with his bike during a key climb. He was criticized for showing a lack of sportsmanship, but it ultimately settled the race.

But the thrill of that win was short-lived as the cloud of doping suspicion soon hovered over Contador.

Weeks later, results showed a positive test for clenbuterol on the second rest day of last year's race, and traces of the drug were found in tests performed over the next three days.

Spain's cycling authorities dismissed those tests because clenbuterol takes several days to leave a person's system, accepting his explanation that he inadvertently consumed very small doses of the substance in contaminated beef.

Flanked by Saxo Bank team boss Bjarne Riis and his teammates during a news conference Thursday in Les Herbiers, Contador gave a curt answer to a question pertaining to the doping suspicions surrounding him, and whether he should be allowed to race.

"I always said very clearly that I am always against doping, zero tolerance, but you can think what you like," he said.

Tour director Christian Prudhomme finds it "hard to understand that a year later, we still don't have an answer," while the UCI has deplored "excessively long" proceedings in Contador's case.

It was scheduled to be heard in June, but CAS pushed the dates back to August, accepting that Contador's legal team needed more time and clearing the way for him to start at Passage du Gois La Barre-de-Monts on Saturday.

Riis -- who has admitted using banned substances when winning the 1996 Tour -- claims that Contador is actually the victim.

"The system is working like that, and I believe we have to respect the system as it is," Riis said. "Alberto was cleared by the system and he has all his rights to ride. ... If you don't agree that Alberto is riding the Tour then you should question the system, and not us."

If CAS rules against him, Contador would lose all his victories since the positive test, including last year's Tour title and the Giro d'Italia in May.

"I am confident in the decision that will be taken after the Tour. (Otherwise) I think it would be completely ridiculous," Contador said. "I am surely the most tested rider, and winning almost every race I am taking part in. I am sure it will be the case at the Tour de France where I will (again be) one of the most tested riders."

Despite the doubts, Contador's legacy could grow.

He is one of only five riders to have won all three of the sport's Grand Tours: the Tour, the Giro and the Spanish Vuelta. A fourth Tour win would give him his seventh Grand Tour victory, tying him with Armstrong, Miguel Indurain and Fausto Coppi. Only cycling legends Eddy Merckx (11), Bernard Hinault (10) and Jacques Anquetil (8) have won more.

Contador is also gunning for his third consecutive Tour, a feat achieved by only five other men: Louison Bobet, Anquetil, Merckx, Indurain and Armstrong, the all-time record holder.

Contador could also make history by becoming the first cyclist to win three Grand Tours in the same season.

"It's the first time I did Giro and Tour in the same season. I did Giro and Vuelta in 2008, but it's different as there was a lot of time between (those) races," Contador said. "The doubt you can have is how well your body recovers."