Milan fought back from 2-0 down - and a failed penalty from Santiago Giminenez - to set up a nervous finish for Napoli after Luka Jovic's goal.
In the end, it wasn't enough for Milan and Conceicao said afterwards: “Since I have been here, which is almost three months, I never sought excuses about the lack of time to train, but today everything happened.
Milan lost Ruben Loftus-Cheek in the morning after he underwent emergency surgery to remove his appendix.
Conceicao continued: “I woke up at 7.30am to a call from the doctor, Loftus-Cheek was ill. We talked to the players after 12.30, because Malick Thiaw couldn’t play either as he was vomiting, then a little later Rafael Leao felt pain in his calf.
“I had already thought of starting without Leao, so it’s not that he didn’t play because of that. He arrived late from international duty after playing two games, so did Santi Gimenez, I had to take that into account.
“We had prepared the game in a certain way and had to change a lot. Having said all of that, we could’ve done a lot more in the first half, we conceded a goal after a minute, the first 20 minutes were not what we had planned.
“These little things keep happening, I don’t want to call on bad luck, but we really had a horrible day. At least there was a very positive reaction in the second half, we created so many scoring opportunities and I feel we deserved a draw out of this.”
On Gimenez's saved spotkick, Conceicao explained: “There are three players who we have on the list, they train regularly, but I’ve been a player, so I know that at times the decision is made on the field. I think Pulisic was trying to give his teammate confidence, he hasn’t scored in a few weeks, so at that moment I do not want to get involved.
“I think it was a good sign of teamwork that they wanted to do that. I still feel we could’ve got a point from this game with the number of chances we created.”
The Portuguese concluded, insisting: “The team has potential, it has quality, but we must find this balance. We have to press higher and have the courage to do that, but Napoli managed to get through our first press far too easily in the first half.
“I saw a different attitude in the second half, because in football you need quality, but also the courage, desire and hunger to take men on. If you struggle off the ball, then you are not fresh to attack with quality when you do get the ball.
“I have a lot of faith in this squad, it’s a healthy group that wants to change this atmosphere and on Wednesday we have the chance to do that.”