Chief Constable Phil Gormley is already the subject of three investigations by the Police Investigations and Review Commissioner (Pirc).
A fourth complaint, which is understood to have come from Police Scotland’s chief analyst, Lesley Bain, is being assessed by the Scottish Police Authority (SPA).
Mr Gormley went on leave early last month when the second complaint against him emerged, and continues to receive his Â£214,000 a year salary.
At that time, he rejected the allegations against him and vowed to return to full duties when the investigations are complete.
The SPA will decide on Friday whether the chief constable can continue on leave or whether he should be suspended pending the outcome of the investigations.
The Pirc has confirmed the third complaint – from Inspector Aimee Canavan – will be subject to a full investigation.
The complaint is being treated as gross misconduct meaning that, if proved, Mr Gormley faces dismissal.
In a statement, the Pirc said: “The chief constable was given notice on Monday 2 October that the allegations will be investigated. The Pirc is investigating other misconduct allegations about the chief constable, which are ongoing.
“Once each investigation is concluded, the commissioner will submit a report to the SPA containing a summary of the evidence and providing an opinion on whether the misconduct allegations about the chief constable should be referred to a misconduct hearing.
“As all three investigations are live, it would be inappropriate to comment further at this time.”
The Pirc is also investigating complaints from Superintendent Graham McInarlin and Assistant Chief Constable Malcolm Graham, a member of the force’s executive.
Phil Gormley, a former deputy director of the National Crime Agency (NCA), was appointed chief constable of Police Scotland in December 2015.
It was hoped his appointment would lead to a period of calm for the national force, but it has continued to be hit by a series of controversies.
Following Mr Gormley’s decision to go on leave last month, Deputy Chief Constable Iain Livingstone cancelled his decision to take early retirement and is currently leading the force.
The SPA declined to comment on the latest allegations.