From Velonews:

He had a big contusion and the team doctors suggested he not start," said Simone Toccafondi, who works with the team's bike sponsor, Specialized. "He was extremely upset to leave. His shape was really coming up. He wanted to show something to Mr. Leblanc, to show that he's a champion, that he could make it over the mountains."

Cipollini's abandon means he won't be using the special bike the team had prepared for the world champion. For the steep, menacing climb to the Monte Zoncolan summit, Cipollini was going to ride a full-suspension mountain bike fitted with road tires.

--What?? Anyone have an idea of the rationale behind that?