The Spanish capital rivals are due to do battle for the first time in La Liga this season on Saturday, with both teams having made strong starts to the domestic campaign.
Atletico have won all six of their matches in the league, and sit two points and one place above Carlo Ancelotti's Real side.
And goalkeeper Lopez believes that Real will have to exploit small weaknesses if they are to get the better of their fierce rivals at the Bernabeu.
"We face a great team, which is very dangerous," he told bwin.com.
"Atletico have formed a very strong and united group. We must exploit small deficiencies in their game, use our quality and try to impose our football."
Lopez believes that the first derby of the season being at home gives Real an edge, but he stressed that every game is vital for their title challenge, regardless of the opposition.
"Real Madrid always wants to win," he continued. "We cannot afford any slip in any game, let alone in our stadium.
"It's an important game, but so was Elche (a 2-1 victory in midweek) and other games we've played."
