Born in Brescia, Diana is a product of Brescia Calcio's youth system. He made his debuts for the first team in Serie B in 1997, and played his first Serie A game on 31 August of the same year, against Inter Milan. He played one season with Hellas Verona F.C. in a co-ownership deal, helping the side to a final ninth position in the top level, and left for Parma A.C. in 2001.