Napoli were held to a 1-1 draw by AC Milan in the second leg of their encounter on Tuesday, with Stefano Pioli's side prevailing 2-1 on aggregate.
The runaway Serie A leaders have now failed to qualify from four of their five Champions League knockout round encounters.
Napoli have also failed to win in any of their last three matches in all competitions.
The Napoli coach told Mediaset: "We congratulate Milan for this qualification, that must be done because they have played two games managing to capitalise to the maximum [on their opportunities].
"This is a sign of a mature team, of players who know how to choose the moments: when to step on the accelerator and when you have to defend yourself with all the team.
"But I also want to congratulate my players. We played a Champions League campaign of the highest level and we played a good match tonight as well.
"We paid for a little inexperience in reading the moments of the match.
"We played with different players with a little tiredness, starting with Osimhen who had not played for twenty days."
He added: "We weren't good enough inside the penalty area to score, as they did the only time they came in.
"We were in good condition, both mentally and physically [in the first half], then after the break we found players not in condition and forcing our press a few times.
"The league win against Torino made us believe that the championship was a formality. During these two games, we did everything totally differently."
