Andy Schleck's chances of winning this year's Tour de France are likely to become clearer Thursday when the first stage in the high mountains puts rival Alberto Contador's knee to the test. Reigning champion Contador compounded an existing knee pain on Sunday when he crashed, for the fourth time in eight days, on the crash-marred ninth stage to Saint-Flour. The Spaniard expressed his "concern" for the injury on Monday's rest day and following rumours he could quit the race he was keen to declare his intentions on Tuesday. "I don't think I'll be going home, not before the end of the Tour de France," the Saxo Bank rider said at the end of Tuesday's 10th stage. While Contador has looked genuinely worried, Leopard's own climbing ace Schleck is taking nothing for granted. "I haven't heard about it," he said when asked about the widely reported injury. If Schleck has doubts, it is perhaps with good reason. The Luxemburger has finished runner-up twice to Contador the past two years, losing last year by just 39secs -- the same margin he lost to Contador when the Spaniard attacked him when his chain came off his bike on the Port de Bales. As well as his formidable skills on the bike, the Spaniard is also known for his mental toughness. In the face of a hostile Lance Armstrong, his teammate at the Astana team during their bid for glory in 2009, the Spaniard struck a huge blow to all his rivals' hopes when he attacked to win the first mountaintop finish. At Verbier in Switzerland Contador attacked nearly 6km from the top of the 8.8km climb to leave Schleck trailing by 43secs, Armstrong coming home 1:35 adrift and virtually out of the race. If Contador's injury woes are genuine, a repeat is unlikely Thusday. Schleck, on the other hand, could strike out on his own in a bid to leave Contador even further down the standings. Before the end of Wednesday's mainly flat 11th stage from Blaye-les-Mines to Lavaur Contador was 1:41 behind third-placed Australian rival Cadel Evans and 1:30 behind fellow two-time runner-up Schleck. Beginning in Cugneaux stage 12 features three climbs in total. La Hourquette d'Ancizan, making its race debut, is a 9.9km ascent with an average gradient of 7.5 percent. The peloton will climb event higher, to an altitude of 2115 metres, when they tackle the 17.1km ascent of the Col du Tourmalet at an average of 7.3 percent. A 20km descent ensues before the climbers and yellow jersey challengers still in contention tackle the 13.3 ascent to Luz Ardiden at an average of 7.4. After a week of surviving the numerous crashes which have bloodied the peloton, sent victory challengers home and left organisers facing scrutiny from cycling's authorities, Schleck says the race is just starting. He said: "The Pyrenees are hard. Luz-Ardiden is the harder of the two Pyreenean stages, even if there is also another big one at Plateau de Beille (Saturday)."