Luciano Spalletti rued Napoli's inexperience and fitness issues proving costly after being dumped out of the Champions League by Milan on Tuesday.
A late Victor Osimhen strike cancelled out Olivier Giroud's opener in the quarter-final second leg, yet a 1-1 draw in Naples sent Milan through 2-1 on aggregate after a 1-0 win in last week's first meeting.
Spalletti was quick to credit a resolute Milan but suggested Napoli's lack of experience was an issue, coupled with fitness problems after Osimhen returned from injury after missing the first leg.
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."
Napoli have failed to progress from four of their five Champions League knockout rounds, with their only success coming in the round-of-16 tie this season against Eintracht Frankfurt.
Spalletti's side are also without a win in their last three games in all competitions (D2 L1), having gone winless in just three of their 16 previous games (W13 D1 L2).
A Scudetto will still likely follow with Napoli leading at the Serie A summit by 14 points, yet Spalletti acknowledged his side have slipped away after getting too comfortable following a March 19 victory at Torino.
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."
After seeing Frank Anguissa dismissed in the first leg, in which Ismael Bennacer's strike proved the difference in a 1-0 win for Milan, Spalletti was left frustrated with referee Istvan Kovacs.
Spalletti once again voiced his displeasure with the officiating, suggesting Szymon Marciniak should have awarded a first-half penalty for Rafael Leao's sliding tackle on Hirving Lozano.
"Tonight there's a clear penalty on Lozano in the 37th minute, very clearly, his ankle just twists," he continued.
"You can see it very well in the replays. You risk twisting his ankle. It's a penalty you can't miss."