Birmingham City Council leader Mike Whitby is being investigated by the local government standards watchdog over a "schizophrenia" jibe hurled at a Labour opponent.
The Standards Board for England – which has the power to suspend or even sack councillors – has been asked to consider whether Coun Whitby's remarks were in breach of the city council code of conduct, which states that elected members must treat each other with respect.
An official complaint to the board was submitted by John Pearson, a former programme director for mental health services in South Birmingham.
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Mr Pearson hit out over Coun Whitby's verbal onslaught at last month's council budget meeting, where he suggested that Labour councillor Marj Bridle might be suffering from "schizophrenia, delusion and amnesia" because she apparently could not recall her own party's administration of Birmingham.
Mr Pearson, who lives in Kings Norton, said it was important that people in public life did not stigmatise those suffering from mental illnesses.
"I don't see why he should be allowed to get away with it," he added. "It is just not an acceptable thing to say in this day and age."
He also believes Coun Whitby may have further broken the code of conduct by damaging the reputation of his office.
In a letter to the Standards Board, Mr Pearson said: "I spent most of my working life in the mental health services in England, my last post being programme director for mental health services in South Birmingham. I consider Coun Whitby's remarks to be totally unacceptable."
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The Standards Board may decide to reject Mr Pearson's complaint, investigate it itself, or ask the city council's own standards committee to investigate.
A spokeswoman said: "We cannot comment on individual cases until we have decided whether a complaint should be investigated further. We will carry out an initial assessment, which will take about ten days."
Coun Whitby (Con Harborne) has already issued a partial apology, after the mental illness charity MIND said it was concerned by his remarks. He had not intended to upset anyone. A spokesman said last night that Coun Whitby would not comment while the Standards Board was considering the case.