Cuellar insists Manchester United defender Nemanja Vidic should have been sent off during the Carling Cup Final.
Referee Phil Dowd awarded Villa a penalty, that James Milner converted, after Vidic had hauled down Villa striker Gabriel Agbonlahor inside four minutes.
No further action was taken against the Serbian defender.
Cuellar said: “For me it is a penalty and a sending-off. I think everyone says the same.
“You saw the sending-off of (Juliano) Belletti of Chelsea for something similar on Saturday. I think this was even more clear.
“But different referees make different decisions and you never know what would have happened had we had the extra man.”