The Netherlands midfielder bagged an important equaliser for Filippo Inzaghi's men on Sunday as they came from behind to draw 1-1 with Sampdoria.
With their European hopes looking slim, De Jong concedes the clash with Roberto Mancini's side will be massive but was encouraged by the second-half showing against Samp.
"For all of us - fans and players - the derby is like a final," he told Sky Sport Italia.
"We played with heart for the last 15 minutes. It's a shame we didn't take the full three points. But we're thinking about the next game.
"We have another eight games. It will be difficult [to qualify for Europe] but we have to keep growing to reach our goal."
The 30-year-old refused to discuss his own future at San Siro, insisting a decision will be taken towards the end of the season.
"I don't want to talk [about my future]," he added to Mediaset Premium. "At the end of the season, we'll see. I want to finish this season with a lot of heart for Milan."