Papadopoulos was called for the under-19 Greek national team to participate in the Elite round of the 2007 UEFA European Under-19 Football Championship. He participated in all three group games against Moldova, Netherlands and Russia, helping Greece finish top and qualify for the finals. Papadopoulos later featured at the heart of the Greek defence in the finals tournament and was partners with teammate Konstantinos Lambropoulos. He was instrumental in keeping a clean sheet against the Czech Republic, as well as strong performances against England and Italy. His performances attracted attention from scouts of elite teams such as Manchester United, Arsenal and Chelsea.