Ac Milan made a mistake by allowing themselves to be defeated by a team that they will defeat without exerting themselves. I don't believe Ac Milan will be able to qualify for the Champions League the following season because it will be very difficult for them to meet up when the league is about to end. On the other hand, Inter Milan made more of an effort to ensure that even if they didn't win the league title, they should still be able to qualify.
Lazio is four points ahead of Ac Milan, thus even if they did earn a point, Lazio would still aim to win the remaining games to qualify for the champion league as well. This means that Ac Milan can not reach the necessary number of points to qualify for the champion league the next season.
Losing against Spezia is already a sign that AC Milan will not qualify for the UCL next season. If we are seeing from points, with the remaining 3 matches Milan can make the last 9 points. However, it is impossible for Inter to lose their matches. Even if Inter Milan loses in 2 matches, inconsistencies Milan's performance still can't make me sure that Milan will be able to take advantage from it. In fact, I'm worried that AC Milan will be under pressure which will make them lose points again.