In the second leg match, AC Milan will play away from home and it is clear that Rennes has the advantage in this second leg match, but to be able to get 4 goal advantage is very difficult for Rennes.
Even though Rennes can win, I sure that in this match they will not be able to win absolutely against AC Milan, which clearly already has an aggregate of 3 points, Rennes will eventually be eliminated from the competition.
AC Milan may not appear very consistent in the Serie A competition, especially today they lost embarrassingly against Monza, which is lower middle class team.
But for the Europa League, I can still be quite confident that AC Milan will be able to give the best results and be one of the team that will qualify for the next round.
However, if you look at the domestic league, their performance is very bad, especially after losing to a weak team Monza, a painful defeat with four goals conceded, AC Milan's defense is so weak in the domestic league. From the last two matches which were very different for AC Milan, my prediction is that AC Milan's journey in the European League will not reach the final. Maybe AC Milan will only reach the semifinals, because of its unstable performance.