Madrid continued their poor title defence against Athletic Bilbao, failing to capitalise on Barcelona dropping points earlier in the day.
Ronaldo and Toni Kroos were wasteful in the goalless draw at San Mames, with Ramos getting another red card.
Ronaldo had previously suggested Madrid are not as strong in 2017-18 following the departures of Alvaro Morata and James Rodriguez, however, attacker Isco did not buy into the argument post-match.
“It’s taking advantage a bit, when the results aren’t coming, to say that the squad is weaker,” he said.
“Our squad is just as competitive as last year, and we haven’t had all of the squad available yet because of injuries and that’s important.”