The Phuket Tourist Rescue Centre was notified of the incident at 10:30am.
The fisherman, 74-year-old Rawai resident San Mali, was brought to Chalong Pier, where an ambulance was waiting to rush him to the Accident & Emergency Centre at the yet-to-open Chalong Hospital.
Mr San was later transferred to Vachira Phuket Hospital in Phuket Town.
However, initial reports gave no description of the injuries.
The Italian, 64-year-old Jojo* Nastri, has now been to asked to explain to the Phuket Marine Office and the Chalong Police his description of what happened on the water leading to the collision.
He is also to present to officials all permits and documentation proving the legality of the boat.
At this stage it appears Mr Nastri was alone on the boat at the time of the collision.
The collision is also so far the only boating incident in Puhket that has resulted in injury during the Seven Days of Danger safety campaign for the Songkran Thai New Year holidays.
* The Italian Man's name was later confirmed by police as Giorgio Nastri, not "Jojo" as initally provided.