Zinedine Zidane said he is concerned by Real Madrid's lack of consistency following their shock defeat to Deportivo Alaves.
La Liga champions Madrid were stunned 2-1 by visiting Alaves at the Alfredo di Stefano stadium on Sunday (AEDT).
Lucas Perez's fifth-minute penalty and Joselu's goal four minutes into the second half put Alaves in control before Casemiro reduced the deficit with four minutes of regulation remaining.
Madrid had beaten Inter 2-0 in the UEFA Champions League during the week but were unable to back up that result as Los Blancos lost for the third time in their last six La Liga matches – as many defeats as they had in their previous 42 fixtures in the competition.
It was only the second time Alaves won away to Madrid in La Liga, having previously upstaged the Spanish and European powerhouse at the Santiago Bernabeu in 2000.
"I think that's the problem we are having at the moment. Consistency," said head coach Zidane, who saw star attacker Eden Hazard hobble off in the Spanish capital, told reporters. "That's why we have to try and improve.
"We've had a lot of injuries. We're not going to try to find excuses but that's the reality.
"Hopefully we can get players back for our next game and hopefully we can improve the dynamic in the squad overall because we have to change it. In three days, we've played two completely different games.
"The difference between the Inter game and today is enormous. I don't really have the words to describe what’s happened but I know we're going to analyse the game today and think about changing things for our next game."
Madrid, who have conceded at least one penalty goal in three successive La Liga games for the first time in the 21st century, are fourth and six points off the pace as Real Sociedad and Atletico Madrid both boast 23 points.