Carlo Ancelotti branded the decision to not send off Espanyol's Carlos Romero -- who later went on to score the only goal in his team's 1-0 win over Real Madrid -- as "inexplicable" on Saturday, after the defender apologised for his challenge on Kylian Mbappé.

Romero was shown a yellow card by referee Alejandro Muñiz Ruiz for his foul on Mbappé in the 61st minute, bringing down the Madrid forward with a tackle from behind as he broke away on the counter attack.

The defender later went on to score a dramatic 85th minute winner, with the defeat leaving leaders Real just one point clear of rivals Atlético Madrid at the top of the LaLiga table.

"The decision the referee and the VAR took is inexplicable," Ancelotti told a post-match news conference. "Everyone saw it. The most important thing is to protect the player. It's a clear foul, a very ugly challenge. Fortunately nothing happened in terms of an injury, but the VAR is there for that. It's inexplicable to us that he didn't show a red card."

Speaking after the final whistle, Romero said he had apologised to Mbappé.

"I knew that it's impossible to stop [Mbappé] on the run," he told DAZN. "I did what I could to stop him. The challenge was a bit ugly, I didn't like that, and I said sorry to him."

Espanyol coach Manolo González said there had been no intent on Romero's part to injure Mbappé.

"It was a tough challenge, but it was meant to stop the counterattack, not to hurt the opponent," González told DAZN.

Madrid were also angered by the first-half decision to disallow a Vinícius Júnior goal for a foul by Mbappé.

"The game was difficult," Ancelotti admitted. "We did some things well. We had control, above all in the second half, and we had chances. We had a goal ruled out, we hit the woodwork. We had 20 shots on goal. Espanyol played well in transitions, defended well, they caught us out of shape and they scored."

Madrid defender Antonio Rüdiger was withdrawn with an injury in the 15th minute, ahead of a run of games which will see Madrid play Leganés in a Copa del Rey quarterfinal, before hosting rivals Atlético in the derby next Saturday, and then visiting Manchester City in the first leg of their Champions League knockout phase playoff.

The team are already without Dani Carvajal and Éder Militão in defence -- while David Alaba has only just returned from a long-term absence -- with the transfer window set to close on Monday.

"Rudiger has a muscular injury, now we'll have to assess it," Ancelotti said. "We've talked about [signings], we've thought about it and we know what we have to do."