The club's assistant boss feels the San Siro side have every reason to be satisfied with their season if they secure Champions League qualification
The Rossoneri initially struggled to find their best form this season, but have climbed into the Champions League places following a string of good results in the second half of the season and can secure qualification if they beat 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.
"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 hold a two-point lead over fourth-placed Fiorentina.