The 31-year-old goalkeeper has been officially unveiled by Los Merengues after re-joining the club from Sevilla on a four-and-a-half-year deal.
"I have come here to give everything from the start and I am ready and in in condition to play on Wednesday," said Lopez
"I have confidence in myself and feel calm."
Madrid moved to re-sign the keeper after Iker Casillas was ruled out for several weeks with an injured hand and he will give coach Jose Mourinho an additional option, despite having never spoken with his new boss.
"I have had no contact with Mourinho," Lopez continued.
"It was my agent that dealt with everything and kept me informed with how things were going."
Lopez came through the ranks at the Bernabeu after originally joining from Lugo in 1994 and will vie with Adan for a starting place against Barca in midweek.
After making just two first team appearances while back-up to Casillas between 2005 and 2007, the Spain international joined Villarreal and then Sevilla.