Why did Alberto Contador not participate in Tour De France in 2006?

Explanation

Alberto Contador Velasco (born 1982) is a Spanish professional cyclist. He started his pro career with ONCE in 2000, and had his first break-through in 2005 with the team Liberty Seguros. Contador won Tour de France for the first time in 2007, whilst on the Discovery Channel team. In 2008, he did not participate, as his team, Astana, were not welcome due to some doping episodes. Contador won the Tour de France again in 2009 and 2010. In 2011, he changed to Team Saxo Bank-Sungard.