The hearing was adjourned until November 20, when Premier Giuseppe Conte has been summoned as a witness.
The court has also called foreign minister Luigi Di Maio, who was vice premier at the time of the standoff, as well as the current interior minister and the former defence and transport ministers.
Mr Salvini, who has largely faded from the public spotlight since being ousted as a minister, has turned the preliminary hearing into a political rally of sorts, staging days of events in a piazza in Catania to rail against Mr Conte’s government.
The Senate voted in February to lift Mr Salvini’s parliamentary immunity, paving the way for a possible trial on charges of kidnapping and abuse of power.
The Gregoretti was stuck at sea for days in July 2019 until a judge approved its landing in Augusta, Sicily.
The Senate has also lifted his immunity in a second case, in which he is accused of refusing to allow 164 migrants off a rescue ship in Sicily.
A preliminary hearing in that case is pending.
During his 14 months as interior minister, Mr Salvini repeatedly denied ships carrying rescued migrants access to ports.
The policy resulted in numerous standoffs, leaving migrants stuck at sea for many weeks before European countries could identify a willing port or courts intervened.
Mr Salvini says he wants to face charges in both cases to clear his name.
Yet he fought to maintain immunity in a third case that was brought while he was still minister, winning protection from prosecution for not allowing 190 migrants off another coast guard ship in August 2018.
Mr Salvini remains the head of Italy’s most popular party, even if it has shed about 10 percentage points in opinion polls since the 2018 elections.
The slide began when he lost his cabinet post in a failed bid to topple the Italian government in August 2019.
Instead, the 5-Star Movement formed a new coalition with the centre-left Democratic Party, pushing Mr Salvini’s League into opposition.
