Claiton started his professional football career at Bologna and played once in Serie A, on 17 June 2001. Bologna lost to Internazionale 1−2. In January 2002, he was signed by A.C. Milan and played for their Primavera team. On 18 December 2002, he made his debut for the club, coming in as a substitute for Alessandro Costacurta in the Coppa Italia 1/8 finals against Ancona. He was also featured as an unused bench for Milan in Serie A on 24 May 2003, the game right before the 2003 UEFA Champions League Final and 2003 Coppa Italia Final, in which Carlo Ancelotti used 4 youth team players in the starting lineup and another 7 players on the bench. In 2003-04 season, he remain the member of U20 youth team.