Henri Leclerc said Strauss-Kahn met the women at swinger parties, The Daily Telegraph reported.
"At these parties, people were not necessarily dressed, and I defy you to tell the difference between a naked prostitute and any other naked woman," he said.
Strauss-Kahn was arrested last year for allegedly raping a hotel housekeeper in New York. But the charges were later dropped.
Now his name has surfaced in an investigation into a prostitution operation that was allegedly based at the Carlton Hotel in Lille in northern France. He denies having paid sex -- or at least sex he knew had been paid for -- although he acknowledges participating in sex parties arranged by others.
Strauss-Kahn resigned from the IMF after his arrest last year. He had been considered a likely candidate for president of France on the Socialist ticket.