Scott MacIntyre, the former spouse of Ford's sister Kathy, filed a lawsuit against the mayor Wednesday, the Canadian Broadcasting Corp. reported.
The lawsuit alleges Ford conspired with his former high school football team colleagues to have MacIntyre beaten while he was in custody, over what MacIntyre knew about the mayor's private activities.
MacIntyre's lawyer, Tim Gleason, has called for an official police investigation into the allegations.
"It is evident that a violent crime was committed," Gleason told CBC News. "It should be investigated."
Toronto police spokesman Mark Pugash said Friday police will not investigate the alleged incident unless MacIntyre files a complaint.
Gleason said it is understandable if MacIntyre is reluctant to file a police report.
"You can see why someone would be reticent in ratting out the culprits if he thought he was to be exposed to that again," he said. "Particularly where, whoever was in charge of him, failed to protect him."
Ford has 30 days to file a statement of defense in the lawsuit against him.