Theodoridis started his career at the academies of AEK Athens and was promoted to the men's team in 1969 with the renewal of roster attempted by the then coach, Branko Stanković. He was a central defender unusual for the time, since he was good with the ball at his feet and had good positioning, resulting playing also as a right back.
Theodoridis began his professional journey at AEK Athens' youth academies before being promoted to the senior men's team in 1969 under coach Branko Stanković. His unique blend of defensive skills and ball control made him an exceptional central defender, who also showed versatility by playing on the right flank.