Louis-Dreyfus, the Russian-born chairwoman of global trading house Louis Dreyfus Commodities, said she would sell Marseille to the best long-term investor.
"The price is not my first concern. However, the capacity of the new shareholder to build a team capable of winning at the highest level is essential," she said in a statement obtained by BFM TV. The club's management confirmed the contents of the statement.
A source close to the club, whose sale has been rumoured in the past, said several offers had been made in recent weeks.
Marseille, European champions in 1993, are struggling this season, lying 14th in top-flight standings and only six points clear of the relegation zone.
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Louis-Dreyfus, who has injected tens of millions of euros into the club in recent years, said a club backed by an individual like herself was no match to rivals supported by governments or specialised sports firms with deeper pockets.
Louis-Dreyfus took control of the club after the death of her husband Robert in 2009.
Marseille won the last of their nine French league titles in 2010.
(Reporting by Jean-Francois Rosnoblet; writing by Leigh Thomas, editing by Ed Osmond)
