The Office of the Independent Review Director also said use of its investigative report could lead to a "chilling effect" on the participation of complainants, witnesses and officers in probes of complaints against police.
"This, in turn, will have a negative effect on (our) ability to fully and fairly investigate a public complaint," director Gerry McNeilly said in submissions.
More importantly, he said, findings of misconduct can only happen after a hearing in which evidence is called, witnesses are examined and cross-examined, and submissions are made.
"Accordingly, the (director) has concerns about the investigative report being admitted for its truth," McNeilly said.
The report in question urges disciplinary charges against Const. Michael Adams and four other officers over the "discreditable" arrest of Adam Nobody at the turbulent G20 summit in June 2010.
Nobody suffered a fractured cheekbone and nose in the arrest, which was videotaped by a bystander.
The family of Junior Manon, 18, of Toronto, who died seven weeks before Nobody's arrest, says the report is relevant to the inquest into his death.
The teen suffocated during his arrest May 5, 2010, following a traffic stop in which Adams and another officer were involved.
Manon's family, which is also suing the Toronto police force, argues there are "striking similarities" in Adams' use of force against Nobody and Manon which may demonstrate a "systemic police failing."
Julian Falconer, who represents the Manon family, told the hearing he would be content to cross-examine Adams on a statement he gave in the report rather than have the entire document entered as evidence.
Adams, who became a police officer in 2008, punched both Nobody and Manon based on his claims the victims were resisting violently.
However, witnesses over the past few days contradicted Adams' account to investigators that Manon resisted like "Superman."
"Please, I'm not resisting," one witness cited Manon as saying.
"Const. Adams is lying," Falconer said. "It's a pretext to justify his own violence."
Falconer called both Manon and Nobody "victims" of Adams.
"There is something wrong with officer Adams' training or how he understands his training," Falconer said.
Like the complaints director, Adams' lawyer Gary Clewley urged the presiding coroner, Dr. Dan Cass, to reject the family's request.
"This motion is an invitation to travel down the route of irrelevance and will sidetrack the (coroner's) jury," Clewley said in his submissions.
Clewley told Cass it would be unfair to allow Falconer to "cherry-pick" evidence related to Nobody's arrest by only cross-examining Adams and not everyone else involved.
The lawyer also noted the officer had not yet been tried under the Police Services Act, and that the province's Special Investigations Unit found no grounds to charge anyone criminally in Manon's death.
Clewley said the job of the inquest jury was to decide how Manon died, not find fault or lay blame.
"We're not here to hold trials within trials," Clewley said.
Miriam Saksznajder, the lawyer for the complaints agency, said it was up to Cass to decide if Falconer could cross-examine Adams on the Nobody arrest.
But to maintain the "integrity" of the complaints process, Saksznajder said the contents of the investigative report should not be part of that.
Coroner's counsel Frank Giordano disputed Falconer's assertion of "striking similarities" between the Manon and Nobody incidents.
Giordano said the inquest jury would be "distracted" by allowing irrelevant but powerful evidence about Adams' role in Nobody's arrest.
Cass reserved his decision.