"It would be a bad generalisation to place the whole clergy and Catholic Church under suspicion," the Roman Catholic priest was quoted as saying in an interview with The European, a Berlin-based online news service, according to an ENI report in Insights.
Mr Küng also said he still agrees with Pope Benedict XVI on some key issues, said the report.
The 83-year-old Swiss-born theologian was speaking two weeks after criticising the Pope in an "open letter" to Roman Catholic bishops worldwide in which he said Benedict's papacy had "failed", and that clerical sex abuses had been covered up worldwide.
However, in his interview with The European, Mr Küng described as "complete nonsense" claims that the present Pope is "the worst for centuries".
He said, "In the course of its five years, this pontificate has seen many breakdowns, as well as many wasted chances, above all in its approach to Protestant churches.
Mr Küng believed the Pope had missed an opportunity to consolidate links with Jews and Muslims, but said it would be "totally inadmissible" to compare Benedict XVI with "immoral and criminal" popes in history.
"The Pope and I are united on the relationship between reason and science, the necessity of dialogue between religions and the need for worldwide ethics, even if my hopes of a reformist course have not been fulfilled," Mr Küng said.SIC: CTHAU