Papastathopoulos joined AEK Athens from Apollon Petalidiou. On 26 October 2005 he made his debut for AEK Athens in a Greek Cup match against PAS Giannina scoring in the 7th minute of the game leading AEK Athens to a 3–0 win.
Loan to Niki Volou
In January 2006 he was loaned to Greek Second Division club Niki Volou for six months in order to gain first team football and gather valuable experience. He made a total of 15 appearances for Niki Volou.