Humbert was detained for questioning on Monday by France's financial crime unit over alleged insider trading at Airbus parent EADS. The judge could decide Wednesday to charge him or make him an "assisted witness," an intermediate stage between being charged and named as simple witness.
Former EADS chief executive Noel Forgeard and the company's former general manager, Jean-Paul Gut, have already been charged in the probe although both have denied any wrongdoing.
The French financial market regulator, AMF, in April alleged in a report that Humbert sold 160,000 shares in the European Aeronautic Defence and Space Company in November 2005, earning €1.685 million ($2.7 million). He is suspected of having benefited from privileged information on EADS' financial prospects as well as delays to the Airbus A380 superjumbo project, which were announced in June 2006 and caused the stock to fall sharply.