Napoli host Barca on Tuesday night for the first-leg of their Champions League round 16 tie.
“We are playing against a great squad," Gattuso said at a press conference. “I thank the team and [Carlo] Ancelotti, I haven't done anything. The emotions are there, but then they pass.
“After [coach Quque] Setien arrived, Barcelona are doing what they had been doing for years. With [Ernesto] Valverde, they won the ball back after 10 seconds, but with Setien it only takes six.
“We need to play a great game in both phases tomorrow, they are coming to assault us. We risk a lot tomorrow."
He continued: “You need to stand up to Barcelona, you can't be worried. I want to see a lively team that plays with joy until the end.
“I read that we have to man mark Messi, but it's not only him. Lorenzo has said that he's a great player, he's not only great at a footballing level. He is the greatest for how he has lived his career. He's an example for the kids to follow, never says anything inappropriate.
“He does stuff that you only see on the Playstation, things you can't even imagine. He's been the best ever for years now."