The AC Milan vs Tottenham match in the Champions League will be held in about 2 weeks from now.
2 weeks are long enough to fix minor issues but it is too short and is not enough to fix major problems.
So that the current performance of the two teams cannot be a strong reference for later. But AC Milan might indeed be the favorite in this match. because AC Milan hosted the match. But we also need to know that currently AC Milan's performance has decreased slightly. even lately AC Milan has not won back either in Serie A or in the Coppa Italia. Even in Serie A AC milan has suffered a big defeat by Lazio with a score of 4-0.
From latest performances from AC Milan, they are likely facing with major problems that need more than 2 weeks to resolve. Tottenham in contrast, have very good form recent weeks and they will likely be able to maintain it until the match with AC Milan in Champions League.
But as I said that the last 16 match for AC Milan vs Tottenham will take place in 2 weeks from now. so maybe at that time AC Milan will return to their best performance again. But if until then AC Milan don't show their best form again then I think Tottenham will probably win the last 16 match later.
It is only your hope and I think your belief is untrue. AC Milan likely have something serious in their team and not only because of temporary form so that they will hardly to fix it all within 2 weeks.
Compare their latest forms and their problems especially AC Milan, I think Tottenham should be considered as a stronger team in their first-leg match even it will be hosted in San Siro, a home stadium of AC Milan.