Real Madrid dropped to second place in La Liga with a 1-0 defeat at 10th-placed Levante in a match that saw Eden Hazard limp off with an injury on Saturday.
The result puts the Bernabeu side, who entered the day with a point cushion atop the table, two points behind new leaders Barcelona who won 5-0 earlier in the day.
With the oft-injured Hazard making consecutive starts for the first time since November, Real were unlucky not to convert a pair of gilt-edged chances in the first half.
Zinedine Zidane was forced to bring on the youthful Vinicius Junior for a hobbling Hazard in the 67th minute, then it was Levante who scored the breakthrough on 79 minutes, with Jose Luis Morales sensationally beating Thibaut Courtois with a sweetly hit left-footed shot from a difficult angle outside of the box.
Madrid will face Manchester City in a Champions League round-of-16 first-leg tie next week and could be without Hazard, who had recently returned from a foot injury, if tests on Sunday show he has picked up a serious injury.
"It's bad, it doesn't look good because he hurt himself where he was injured. It's a knock, not more than a knock, but we'll see if it's not much," Zidane said of the injury after the match. "Right now it hurts him, and we'll see tomorrow when we do more tests."
The Belgium international has played in just nine of Real's 25 league games this season but in five of their six Champions League matches. Hazard, who joined Los Blancos from Chelsea for £88.5 million plus bonuses last summer, has scored just once in all competitions.
"Apart from the result, there's the injury to Hazard," said Real defender Sergio Ramos. "Let's hope it's not too much and it's not as serious as the first one. He'll undergo tests and let's hope he returns as soon as possible because it seems like just when he's well and can help the team, unfortunately, he suffers another injury."
Ramos, who was cautioned in the 10th minute for a hard foul, then took aim at referee Alejandro Jose Hernandez Hernandez, with whom he's had history over the years.
"With this referee, honestly, it doesn't surprise me at all," Ramos said of his yellow card. "I'm annoyed because it's an unpleasant situation, getting a card in the 10th minute conditions the game. I got elbowed and then I won a disputed ball and I got a yellow.
"It makes you think, it seems like it's predetermined. Before, you could talk to referees... you should always show respect and manners. There are some referees you can't say anything to... It's outrageous, really, on a personal level. At the end of the game I asked him if it was personal, if it can be solved, I don't know what the reason is."