City rivals Inter were beaten by Manchester United in the last 16 of the Champions League.
“If we had faced United we would have won,” Gattuso told the Corriere dello Sport.
“The Champions League is always unpredictable and it is crucial that we regain our place in the competition. One year in the UEFA Cup is enough for us.
“If we can beat Napoli then we should finish third.
"However, we will need to galvanise the squad in the summer because if Paolo Maldini retires and we don't keep Giuseppe Favalli then we need another defender to help Thiago Silva out.”