The comments follow last week's suspension of Adrian Gregory as headteacher of North Manchester School for Boys following a verbal report from Office for Standards in Education inspectors. Mr Gregory is to face a disciplinary investigation ordered by the governing body.
The OFSTED report, due out later this month, is understood to be highly critical of teaching standards and management of the school, which suffers the highest truancy rate in the city.
Labour-controlled Manchester council has shared these concerns for some time, and advised the governors to suspend Mr Gregory, it was revealed this week. Roy Jobson, the council's director of education, said staff absence, poor examination results and truancy were among the worries, and Mr Gregory was suspended to allow a full investigation to take place.
But John Sutton, general secretary of the Secondary Heads Association, of which Mr Gregory is a member, said: "There is no justification for suspending someone from their job because of an adverse OFSTED report. No offence has been committed and it is an inappropriate use of procedure."
Last year, the National Association of Head Teachers found the number of heads suspended by governing bodies had doubled in one year to 68 cases.
NAHT general secretary David Hart said: "It is far too easy for governors to treat heads as scapegoats when a school is given a poor report. The head exercises enormous influence and questions may need to be asked about their performance, but it should be part of the inquiry leading to an action plan.
"Too often governors go in for football manager syndrome - they think firing the head will cure the school's ills. OFSTED reports are not about misconduct but competence and it is wrong to use them as grounds for disciplinary measures."
Mr Jobson said: "The school is facing a number of difficulties and given the number of adverse statements and allegations being made about the head's performance, it was felt it would be better to start the new term with him suspended in order to work through the issues." He said he had no evidence of governors in any Manchester schools treating heads as scapegoats.