The goalkeeper acknowledged that his side's first-leg win was impressive but added that his team will need at least another goal to guarantee progression.
“Clearly 3-0 is a very good result for us, but I think the key to the next game is getting another goal,” he told Bwin.Lopez, signed in January following an injury to Iker Casillas, also said he expected a different Galatasaray to the one that played in Madrid.
“It's a difficult place to go against a good team. They did not show their best side, they are better than they were in the first leg.
“They are a very good team who can hit us on the counter-attack. We have to keep our composure defensively.
“I am expecting a tough match in a tough environment”
With the league almost certainly heading back to Barcelona, the Champions League and Copa del Rey represent the only opportunities Real Madrid have for silverware this season.