Fiat Chrysler's (FCA) shares fell 12 percent this week. However, the stock tumbled 15 percent on Wednesday alone when the carmaker issued a profit warning and released weak second-quarter results shortly after the announcement of Marchionne's death.

"No anomalies have emerged from the regular checks performed so far," one of the sources said.

The second source added that the way FCA had informed the market about Marchionne's ill-health and later his death appeared to be in line with rules.

Questions have been raised about how long Marchionne, 66, had been ill and how much the company knew before it made the situation public.

A Swiss hospital said on Thursday it had been treating the deceased chief executive for more than a year.

FCA said Marchionne's family had informed the company on July 20 of the serious deterioration in the chief executive's condition and that he would not be able to return to work.

The company announced succession plans for the longtime CEO the following day.

(Reporting by Massimo Gaia and Paola Arosio, writing by Agnieszka Flak; editing by David Evans)