The Colombian defender has struggled to earn a place in Filippo Inzaghi's side, having dropped down the pecking order at San Siro.
However, he returned against Inter on Sunday as Milan earned a point from a 1-1 draw against their city rivals, and he is now hoping that is the start of a long run in the team.
"I hope to become a first-team regular again soon," he told Gazzetta dello Sport. "Because it's hard to find form without continuity.
"The back-line has hardly ever been the same and when you frequently change the players, it's hard to find a balance.
"I myself know that I have had some negative displays. Against Palermo for instance it all went wrong (Milan lost 2-0 and Zapata scored an own goal).
"I know that I still have a lot to prove, but I have no doubts over my qualities."
"We have to start winning right away," he added. "As only by winning will we get back into the Champions League.
"The derby was a missed opportunity. Not obtaining a result for Milan means lots of pressure is heaped upon us."
