Napoli go into the last-16 tie, which starts with a home first leg on Tuesday, as clear underdogs to progress.
But Gattuso wants his team to show belief and, amid reports his players would try to isolate Messi from the rest of his team-mates with a unique man-marking strategy, insists there is only so much you can do to stop Barca's talisman.
"You need to stand up to Barcelona," head coach Gattuso said at his pre-match news conference.
"I want to see a lively team that plays without worry and with joy until the end. I want a Napoli side that are not afraid.
"We haven't played great at the San Paolo in recent weeks, except against Juventus, so I want to see a team that knows how to battle. It is fair to have respect for the opponent, but not fear.
"I read that I would prepare a cage to stop Messi. It is not so, we need the collective to play the game and remember that there is not only Messi on the field.
"Lorenzo Insigne said that Messi is a great player. He does things that I see only those who play the Play Station do, he has incredible quality.
"And he's not only great at a footballing level. He is the greatest for how he has conducted his career. He's an example for kids to follow. He never says anything inappropriate.
"You can't stop Messi, but in these moments my players have to try. We are playing against Barcelona, it is not only Messi.
"It doesn't make sense to have a player man mark Messi but we will try some things in training and then we will see."
Referring to Napoli icon Diego Maradona, Gattuso added: "He was the god of football, I saw him in many videotapes, but never live.
"I know, however, the champion that Diego was, certainly one of the biggest in the world.
"Right now, Messi is the one who comes closest and does some of the things he did. I'm sorry I didn't see him live, I missed something wonderful.
"Barca have some important players missing, but Quique Setien is a great coach and with him they have returned to many of the things they did in the past. They win the ball back so quickly. We know it will take a great performance to win.
"Can Napoli win the Champions League? Never say never. I thank the team and Carlo Ancelotti for their work as I haven't done anything to get here, but now I am excited."