Real Madrid coach Rafael Benitez has restated his support for French striker Karim Benzema amid increasing criticism of Benzema's off-field behavior in his homeland.

Benzema has been charged in France for his alleged participation in a blackmail case involving international teammate Mathieu Valbuena over a sex tape.

French Prime Minister Manuel Valls added his voice to the debate on Tuesday by claiming sportsmen who don't behave in an "exemplary" manner should not play for the national team.

However, Madrid has insisted it will stick by Benzema and Benitez said the 27-year-old remains a key player despite not starting either of Real's past two outings.

"I consider him a fundamental player for us. On a personal level I have said before that he is a great guy and he has our support," Benitez said on Tuesday.

"He is a key player for us because he is a reference up front and makes those around him play even better."

Former France international striker Djibril Cisse, who was himself interviewed by police investigating the sex-tape affair, said Benzema deserved to be assumed innocent until proven guilty.

"For the moment he's being investigated but he hasn't been judged and hasn't been found guilty," Cisse said.

"Give him the benefit of the doubt, the time to explain and let justice run its course.

"Like a lot of French people, I'm waiting to see what he has to say. But I'm not here to savage him and I leave it to the law and the police to decide."

Benzema started Madrid's humiliating 4-0 defeat at home to Barcelona 10 days ago after a six-week absence due to a hamstring injury, but was only introduced as a late substitute in wins away at Shakhtar Donetsk and Eibar in the past week.

"He is very important for us. He had a long time out with injury and we have to manage his minutes the best way possible." said Benitez.

Benzema will miss out once more when Madrid opens its Copa del Rey campaign away to Cadiz on Wednesday as Benitez has left a host of star names back in the Spanish capital.

Cristiano Ronaldo gets his first rest of the season, while Gareth Bale, Luka Modric and Toni Kroos have also not traveled.

Benitez is in need of a big performance after two unconvincing displays despite bouncing back from the Barcelona debacle with consecutive wins.

However, he insisted that winning rather than beautiful soccer is the most important way to make amends with the fans.

"First we have to define what is beautiful and good football," he said.

"In principle, what Madrid have to do is respect Cadiz, who are an historic team in Spanish football, and respect such a difficult and dangerous competition as the Copa del Rey.

"We need to prepare for the game with good concentration, with desire, give our best, which is what Real Madrid fans always demand, and on top of that play as well as possible and win."