Three other men were placed under formal investigation after Mr Valbuena was contacted by someone claiming to have the tape.
Mr Benzema`s lawyer said he wanted to clear his name.
"When his name was mentioned by the press, Karim Benzema immediately let the investigating judge know he was available to investigators," lawyer Sylvain Cormier told Le Parisien newspaper.
A friend of the striker was quoted as saying there was no way he would be placed under formal investigation.
Another former footballer, Djibril Cisse, was detained briefly last month but was later released without charge.
Training chat
According to French reports, Mr Benzema mentioned the video to Mr Valbuena during a national team training session at Clairefontaine in early October, ahead of matches against Armenia and Denmark.
It was unclear whether he was offering friendly advice or trying to press his team-mate to pay the blackmailers.
Sources told French media that one of Mr Benzema`s relatives was contacted by the blackmailers, who attempted to involve the player in their scheme.
French TV channel M6 reported that a close friend of Mr Benzema`s brother was also taken into police custody on Wednesday.
In calls with police posing as Mr Valbuena`s business associate, the blackmailers threatened to release the video ahead of the 2016 European Championship in France.
Three men were arrested, one of whom was close to Mr Valbuena and had direct access to his phone, which contained the tape.
It is not the first time Mr Benzema has been involved in a police investigation. Last year, he and his teammate Franck Ribery were cleared of accusations they had slept with an under-age prostitute, who later went on to become a reality TV star and fashion designer.
More about:
