The 27-year-old has reportedly already agreed to a four-year deal with Lens, although a fee has not yet been struck.
Martel is unhappy at how negotiations have been progressing, but is hopeful a solution will be reached with Le Mans.
"I would like to settle Daniel Cousin's transfer quickly," said Martel. "Talks are not easy with Le Mans, but I have hope."
In what is set to be a busy summer for Lens, the club are believed to be closing in on Eric Carriere to replace Daniel Moreira.
Moreira has joined Toulouse on a three-year deal and now Lens want Lyon playmaker Carriere, who has won four Championnat titles.
Meanwhile, Dagui Bakari could leave Lens and join newly promoted St Etienne on loan, although Swiss outfit Grasshopper Zurich are also interested.
"Regarding Dagui, we've had several loan propositions from French and foreign clubs. We are currently studying them," concluded Martel.
