The AEK Athens player used the salute while celebrating the winning goal in a 2-1 victory six minutes from the end of the game against Veria.
EPO said in a statement the player's gesture was "a deep insult to all victims of Nazi brutality."
The 20-year-old midfielder later apologized but said he was unaware of the significance of the gesture.
Katidis said he trying to devote the goal to a team-mate sitting in the stands and was pointing to him and trying to get spectators to stand up./DPA