Karim Benzema celebrates his second goal against Mallorca (AFP)
Real enter the weekend 10 points clear at the top of La Liga. They are 15 points ahead of third-place Barcelona, who they host on Sunday evening.
Benzema was included in the France squad announced on Thursday by Didier Deschamps for friendlies against Ivory Coast on March 25 and South Africa on March 29.
"We never take risks with him," said Ancelotti. "He still has some pain. It's a small injury, but it prevents him from training and playing,"
The international break allows Benzema more time to recover.
"We will have two weeks to prepare him for the end of the season, where he will be very important, as always. He's always come back from little glitches like this, and he's always made a difference."
Benzema scored twice on Monday in Mallorca to take his career total to 413 goals, breaking a tie with Thierry Henry at the top of the all-time list of French scorers.
Benzema limped off in the 87th minute visibly bothered by a pain in the left calf, leaving his teammates to finish the game with 10 men.
He is by some distance the top scorer in La Liga with 22 goals. Team-mate Vinicius Junior is tied for second on 14.
Ancelotti has plenty of options. Vinicius, Rodrygo and Marco Asensio have played most this season, but the coach could also recall Mariano Diaz, Luka Jovic, Eden Hazard or Gareth Bale.
"Everything is decided, but I will not tell you anything," Ancelotti said.
"We want to be at our best and it'll be a game that involves a lot of different elements. We can't go thinking that doing just one thing well will be enough to win the game. We're going to have to produce a strong all-round performance," he said.
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