Lopez is on-loan at Milan from Catania.
"I am very happy here. I am always at the disposal of the Coach and try to be ready whenever I am called upon," he told Milan Channel.
"Every time I have had the opportunity to play, I have been up to the task. I am fired up and ready to go.
"It will be difficult to win the Scudetto, but we cannot let anything go right now. Siena are tough opponents at this moment, as they are in great shape physically.
"It's a shame we dropped the advantage we had at the top of the table, as we went from being four points clear to three points behind. We've been playing every three days for the last three months and eventually that weighs on you.
"However, it's not over yet and we've got to push, because you never know when Juventus could slip up."