The Brazilian midfielder has admitted Wednesday's defeat was hard to take but remains fully confident his side can beat Atletico Madrid in the return leg
The Rossoneri created a number of chances to go ahead but failed to beat an inspired Thibaut Courtois and were eventually punished for their profligacy in front of goal when Diego Costa broke the deadlock in the closing stages of the game.
Kaka admits the loss was tough to take but insists his side showed they are good enough to win at the Vicente Calderon in the return leg.
"Of course we were left with a bitter taste in our mouths, because we gave a very good performance, with the right spirit. Unfortunately, we did not manage to score," Kaka told reporters.
"We created a lot of chances so we are disappointed, but also confident we can still secure qualification in Madrid.
"In my opinion, the qualification is still open, even if I admit it will be very difficult.
"We must win in Madrid, against a great team like Atletico, but looking at our display tonight I think we have a good chance of doing it."
The return takes place in the Spanish capital on March 12.