The former Real Madrid man says the San Siro side must now put all their effort into improving their Serie A form if they are to qualify for Europe this season
The Rossoneri crashed out after a 2-1 home reverse in the quarter-final and the Brazilian midfielder realises Milan have plenty of work to do if they are to achieve anything in 2013-14.
"It's tough for all of us at the moment. We have a lot of improving to do. It's a tough moment and it's bad to get knocked out of the cup at home," Kaka told the official Milan website.
"There's a chance now that we won't be playing in Europe next season but we should take this as a motivation. It's hard to imagine a Milan side that does'’t play in Europe.
"We're really disappointed. The cup was the best way to get into Europe next season and now we have a tough road ahead of us in the league.
"We have little to talk about and lots to work on."
Milan resume Serie A action on Sunday when they travel to Cagliari. They currently sit 11th in the table with 25 points from 20 games.