The Partenopei crashed out of the Europa League with a 3-2 aggregate defeat to Granada, despite winning 2-1 last night.
"We are disappointed, as we could've done more. It was difficult after the 2-0 first leg defeat, conceding the equaliser today knocked the wind out of us, but we still tried to the end," Koulibaly told Sky Italia.
“We wanted to go forward in the competition and going out today is painful. We saw once again that Granada played with everyone behind the ball."
He added: “There are no more excuses now. Our objective is to get back into the Champions League and we must do everything to get into the top four. It's simply too important for us, we have to reach the top four at all costs."