Massimilliano Allegri's side are just three points behind unbeaten Juve with four games left to play going into Sunday's clash with Sienna, and Lopez believes that the Rossoneri are facing an uphill struggle to retain their crown.
"It will be hard to win the Scudetto, but we are not giving up," Lopez told MilanNews.it.
"It is a shame that we lost the lead we had, because we went from four points clear to being three points behind. We have been playing every three days for the last three months and it is not easy to keep up this pace.
"It is not over yet and we will not give up, hoping that Juventus will slip up."
Lopez, who in on loan at Milan from Catania, has scored two goals in 11 appearances.