Robert Mancini lamented his side's inability to score goals as Italy were held by Northern Ireland at Windsor Park.
The Azzurri failed to break down a resolute home defence to miss out on automatic qualification for next year's World Cup.
Switzerland's 4-0 win over Bulgaria means Italy now face a play-off to determine whether they will be in Qatar.
"I am disappointed, because we didn't find a goal in the first half," Mancini told Sky Sports.
"I think we play a good game, a lot of good possession. But Northern Ireland is difficult because they get all the players behind the ball.
"They are strong and tall, and if you don't score fast it is difficult."
Mancini was left to reflect on last Friday's 1-1 draw with Switzerland, where Jorginho missed a last-minute penalty to snatch all three points.
"I think we played a good game, but this group should have finished last Friday. We had a penalty to beat Switzerland, and the group would have been finished," he added.
"We knew that Switzerland had a lot of chances to win their game. We didn't expect 4-0. But that doesn't change our situation because we didn't score.
"At the minute we have this problem to score goals. We play good football, but we don't score.
"I think we are one of the best teams in Europe. We need to recover well for the play-off, and I am sure we will win the next two games."
