The Rossoneri initially struggled to find its best form this season, but has climbed into the Champions League places following a string of good results in the second half of the season and can secure qualification if it beats Siena on Sunday.
"Third place would be a big achievement after losing Thiago Silva and Ibrahimovic. It would change a lot of people’s opinions," Tassotti told Milan Channel. "It’s been a tough season but we have the chance to end it well."
He added, "There’s a bit of tension but that’s normal ahead of a big match. It’s a decisive match but we've played a lot of those during the season to get to where we are today. We have to stay calm. We have a big chance this weekend which would make this season a successful one for the club."
Milan currently holds a two-point lead over fourth-placed Fiorentina.