French news magazine L'Express published an interview on its website in which lawyer David Koubbi said he would “file the complaint on Tuesday July 5, to the prosecutor, who will receive it on Wednesday morning”.
Koubbi said suit referred to an incident that took place in 2003 when Banon, then 22, interviewed Strauss-Kahn in a Paris apartment.
The news comes three days after US prosecutors said they doubted the credibility of a hotel maid who accused Strauss-Kahn of a separate sexual assault in New York.
Strauss-Kahn was released from house arrest on Friday, prompting speculation within the French opposition Socialist Party that he may return to run for president.
On Monday Socialist Party spokesman Benoit Hamon told French media that the idea Strauss-Kahn could now run for the presidency was “the weakest possible hypothesis”.
Koubbi denied the decision to file a lawsuit was influenced by the New York case. “Even if that case against Mr Strauss-Kahn turns out to be unfounded, ours is not - it is extremely solid and backed-up,” L'Express quoted him as saying.
Banon told a television chat show Paris Premiere in 2007 that a senior politician assualted her after luring her to a virtually empty apartment in the guise of agreeing to give an interview. But in the broadcast version, the name of the politician was bleeped out.
“I put down the recorder straight away to record him. He wanted to hold my hand while he replied,” Banon said at the time, adding that when she refused the pair ended up “fighting on the floor”.
Banon's mother, Socialist politician and blogger Anne Mansoure, later confirmed to French news website Rue89 that she had urged her daughter to hold off filing charges against Strauss-Kahn.
Meanwhile in the United States, prosecutors said Monday they would press ahead with their investigations.