Cristiano Ronaldo will have tests on a potential injury, although Real Madrid coach Zinedine Zidane said he felt "relaxed" about the prognosis.
In second-half stoppage time of Madrid's 3-0 win over Villarreal on Wednesday, Ronaldo walked from the field holding the back of his right leg.
With Zidane having made all three substitutions, Madrid were forced to finish the game with 10 men although it mattered little as they kept pace with Barcelona and Atletico Madrid, who had won earlier.
The sight of Ronaldo walking from the field in discomfort will cause concern among Madrid fans, but Zidane was quick to play down any fears.
"Cristiano felt something at the end. He went off because he wanted to know what it was. It looks like more of a scare than anything else," Zidane said.
"We will have to see tomorrow, but I'm relaxed now. We are concerned, but after seeing him in the dressing room I am less worried.
"He is relaxed. It doesn't look like anything serious. We will see tomorrow exactly what he has.
"A player like Cristiano, sometimes he should rest, not finish a game, or sit it out. But he always wants to be out on the pitch.
"Sometimes, for me, today when I see him coming off pitch, it's difficult. There are important games to come, we'll see when he's back."
There was better news on Gareth Bale, who missed the Villarreal game with a back problem.
"I hope that tomorrow he is going to train with us, and that he will be there for Saturday's game [at Rayo Vallecano]," Zidane said.
