Reports from Papua New Guinea say the higher education minister, Michael Ogio, is to be the acting governor-general, but government representatives would not explain why it was not the Speaker Jeffery Nape.
He replaced Sir Paulias Matane's whose reappointment in June was ruled to be invalid.
The Supreme Court ruling on the governor-general also criticised Mr Nape for his role in the unconstitutional appointment.
According to the newspaper, The National, Mr Ogio will be in the role from Monday.
Meanwhile, the leadership tribunal to look into the case of Sir Michael Somare is not expected until February at the earliest.
He stepped aside as prime minister this week for the tribunal to probe alleged misconduct as a leader over the past two decades.
The courts shut down on Monday for their Christmas break and do not return until the end of January.