Zinedine Zidane says he will have to manage Cristiano Ronaldo carefully after the Real Madrid forward suffered an injury scare.
Ronaldo limped off towards the end of Real's 3-0 victory over Villarreal on Wednesday with a hamstring complaint.
Zidane was unable to replace the Portugal international having used all three of his substitutions, leaving his team with 10 men for the closing moments of the match.
Ronaldo had played every minute of Madrid's 34 La Liga games this season up until last night and has started all 10 matches in the Champions League, only being substituted in the 89th minute of the last-16 first-leg against Roma.
"Once in a while he needs to be substituted so he can rest," Zidane said. "It's necessary for him not to finish one game or to miss one game occasionally.
"But he's a player who always wants to play and give everything he has. It's difficult for me at times."
Spanish newspaper AS reported Ronaldo was suffering from cramp. He is expected to have medical tests on Thursday.
However, Zidane insisted he was not worried that Ronaldo had suffered a serious injury. Madrid are preparing for a La Liga game at Rayo Vallecano on Saturday and their Champions League semi-final first-leg with Manchester City on Tuesday.
"He is more a team player than people think, he is working very well and defending a lot," Zidane added.
"Everyone recognises his work. He doesn't just score goals, he's another member of the team."