Nuala O'Loan's office will need at least an additional six-figure sum to fund investigations into killings carried out by the RUC, The Irish Times has learned.
Under existing legislation the Police Ombudsman is charged with the investigation of dozens of disputed killings in which RUC involvement or misconduct is alleged.
Originally it had been thought that up to 48 deaths involving the RUC before 1998 would be handled by Ms O'Loan's office and not by the newly-established Historical Enquiries Team (HET) which last week began work on more than 3,000 unsolved killings during the Troubles.
However, it is now understood that the total number of cases could rise above that, adding to concerns within the Police Ombudsman's office that not enough resources are available.
Ms O'Loan has already gone on record as stating that the extra caseload arising from the investigation of disputed killings involving RUC officers would mean a substantial drain on already stretched resources.
"I don't know how many there are yet," she said in November. "I think it could double [the existing historical cases total]."
Her office currently works with a budget of more than £7 million annually (€10.3 million), and there are concerns that an additional workload of perhaps more than 50 cases will lead to budgeting difficulties.
The Irish Times understands that some of these cases will be dealt with as "desk investigations" in which officers review the paperwork from historical cases. Others will require much more in-depth investigative work before a satisfactory resolution is arrived at.
Ms O'Loan told the Irish News recently: "Any case which the Historical Enquiries unit have, in which the conduct of a police officer may have led to a death, must be transferred here. That is a very important thing which people don't understand."
She added: "[The chief constable] is under a duty to bring to my attention anything where the conduct of a police officer may have contributed to a murder."
Her office has already raised the question of the current level of resources with the Northern Ireland Office. But if, as expected, the number of retrospective cases doubles, then further budget pressure is inevitable.
The HET, which is reopening 3,268 unsolved murders, has around 100 detectives and support staff and a budget of some £30 million (€44 million).
It is understood that not all unsolved or "cold" cases are clear cut and may be transferred between the Police Ombudsman's office and the HET, further complicating the picture.