Magistrates in Milan and Parma, who are spearheading the inquiry, will question Fausto Tonna and Luciano Del Soldato, as well as Gianpaolo Zini, lawyer for Parmalat's disgraced chief Calisto Tanzi, judicial sources said on Thursday.
Lorenzo Penca, ex-head of auditors Grant Thornton Spa, will also be questioned, a legal source said.
All four were arrested on Wednesday along with three others who are also likely to be questioned in what is emerging as one of the world's biggest corporate scandals.
The company, headquartered near Parma in central Italy, has been declared insolvent and put under the management of turnaround expert Enrico Bondi.
Prosecutors believe Tanzi, helped by an inner circle of advisers, falsified Parmalat accounts for years and embezzled more than 800 million euros, saddling the group with debts they estimate between 10 billion and 13 billion euros ($16.21 billion).
Tanzi was seized last weekend in Milan and has since told investigators that around eight billion euros could be missing from the company's accounts.
He has also admitted siphoning off some 500 million euros from the publicly quoted company to Tanzi-family firms.
Long-standing concerns about Parmalat's opaque accounts exploded into a full-blown crisis two weeks ago when Bank of America rejected as fake a document purportedly showing a Cayman Islands unit of Parmalat held four billion euros of cash and securities with the US bank.
The Italian unit of Grant Thornton certified the accounts of the Cayman Islands unit. It has denied any wrongdoing. A warrant has also been issued for the head of Parmalat's Venezuela business, Giovanni Bonici, who is out of the country.