European Parliament member David Casa appeared before a magistrate on Monday morning as part of an inquiry into leaked Financial Intelligence Analysis Unit reports.
Mr Casa testified before Magistrate Doreen Clarke and later told the media that he would not be revealing who his source was.
"I must defend this person, and I must defend their life, because it may be in danger," Mr Casa said in a video he posted on his Facebook page.
He said that another battle - one by the media - would begin tomorrow, in a reference to the Daphne Files collaboration between 45 journalists from 18 international news organisations, including the Times of Malta.
The media houses, which include The New York Times, Reuters, The Guardian, and Süddeutsche Zeitung, the newspaper behind the Panama Papers, will start publishing revelations from the collaboration on Tuesday.
Mr Casa has said that he is in possession of a leaked FIAU report containing damning evidence of impropriety by minister Konrad Mizzi and the Prime Minister's chief of staff Keith Schembri in connection with the Enemalta privatisation deal. The FIAU has said that the report Mr Casa referred to is not a finalised one.
Former Opposition leader Simon Busuttil has also testified before Magistrate Clarke as part of the inquiry. Following his testimony, Dr Busuttil had said that "many people are suffering because we have a government for whom justice and the law do not count. I will continue to fight for justice in our country."