Diego made his international debut in April 2003 in a friendly match against Mexico. He was later included in Brazil under-23 team that competed in 2003 CONCACAF Gold Cup alongside Santos' teammate Robinho. Although Brazil compete as an under-23 team, the international appearances and goals were recorded as FIFA acknowledge the tournament as senior team matches. He appeared five times and scored two goals as Brazil U-23 lost out to the Mexico senior team in the final.