Siena prosecutors question Mussari in MPS probes on Monday
Ex-chief executive Vigni also called in investigations04 February, 10:28
Prosecutors will also question former chief executive Antonio Vigni on Wednesday.
MPS was thrown in crisis in January when it emerged that a shady series of derivative and structured finance deals produced losses of 720 million euros.
There have also been reports of bribery and corruption by bank officials regarding, among other things, the costly nine-billion-euro acquisition of rival Antonveneta in 2008.
Former chairman Giuseppe Mussari quit as the head of Italian banking association ABI soon after the scandal broke.
He is said to have personally authorised at least one of the derivative operations at the centre of the storm. He denies any wrongdoing.