We don't need a "top coach", Zidane wasn't one either... We need a coach who has the respect of the players, gets them to care and perform and has some kind of useful tactical concept. Lopetegui is playing Zidane's team without its focal point. That makes 0 sense, he should make changes to make it his team and if he isn't up to the task leave. He was the 4th or 5th choice at best as Pochettino, Allegri, Löw and probably some others were offered the job before him.
As far as possible successors the Guti-Raul-Xabi Alonso route would be the most likely and probably the most reasonable one. The question is how dire will the situation have to get under Lopetegui before Florentino kicks him out. I'm sure he feels some sense of moral obligation to him because of how the whole process cost him the World Cup but I don't care about the Spanish national team so for me Lopetegui has one final chance on Saturday. If that game is a loss, too, sack him right then and there.
What people might not realize. We lost one title already with the Supercopa, a game where all the defects we still have were on full display already: Slow start, low physicality in play, no stamina, lightweight attacks, stupid subs, etc. And the last couple of games the curve is showing downhill, we started the league well against teams we have to beat no matter what but then the draw at San Mames against a weak Bilbao side, the win over a very bad Roma side, the lucky win over Espanyol and now this disastrous loss. This wasn't "one bad game that can happen to anyone", this was the logical result of a downturn in form across the entire team in recent weeks.