The Italians are seeking to return to the World Cup for the first time since 2014 after missing the last two tournaments in Russia and Qatar, both following playoff defeats.
Should the four-time world champions get past Northern Ireland, they would face a potential final against either Wales or Bosnia & Herzegovina to qualify for the soccer showpiece in North America.
"Northern Ireland is a physical team, they never give up," Gattuso told Sky Sports Italia after the playoff draw on Thursday.
"We have to play it. I've been saying this for three months. We knew we had to go through the playoffs. We look ahead with confidence."
Italy sacked former manager Luciano Spalletti in June, and while Gattuso led the side to two wins over Estonia and Israel, as well as a victory against Moldova in his first five matches, they were still unable to earn direct qualification.
They lost 4-1 in their final qualifier to group winners Norway.
"Right now, we must work on our fragility because we've proved that when we do things right, we are competitive," Gattuso, 47, added.
"Of course, you can't afford to make mistakes as we did the other night, but this is my priority: improve this aspect."
The World Cup will be held from June 11th to July 19th in Canada, Mexico and the United States.