Lopetegui, though, rejected suggestions Atletico's extra day of rest could give Diego Simeone's men the edge ahead of their short trip to the Santiago Bernabeu.
"One day less doesn't worry me, I don't think about that," Lopetegui told a media conference. "We've got good energy and we're ready so that's more important. The motivation is there, you need motivation for games like this.
"We're on good form even though we didn't have a good first half the other day [against Sevilla]. In general, we're in good shape.
"We've been playing every three days recently and I think the second half against Sevilla was good. The side physically is good, other things and football matters come into play but physically no problems.
"I expect a balanced, demanding game that will be hard. We will have to compete, play as well, but compete. We are ready for this game against a very good opponent who will make things hard for us. That's what we expect, a game of the highest level, we have no doubts about that.
"We can't look for excuses now, the calendar is like that. Energy and motivation have to be above all these things and we have that at the moment going into these games."
"The truth is the perception from outside can be different but they are very motivated to win the league and we are doing well, at the top in a good position but there's a long way to go," Lopetegui added.
"It will be a long season for all the contenders to win the league but motivation is very high.
"I'm happy with what my team has given me. Like all sides sometimes we do things better and sometimes worse, but our analysis after six games is that attitude and the way players go into games with their motivation - there are no doubts whatsoever in my side.
"I just want us to go into a big game and give our fans something to shout about, it doesn't matter if the opponent is Atletico Madrid, the motivation is always the same for a game like this."
Marcelo is expected to miss Saturday's match after Madrid confirmed the Brazil left-back has a calf injury, which could keep him out of action for a few weeks.