Former City of Edinburgh Council leader Cammy Day was accused of sending unsolicited sexual messages almost two years ago, it has emerged.
The Labour politician quit earlier this month after it was alleged he "bombarded" Ukrainian refugees with messages.
He is being investigated by police over an allegation of inappropriate behaviour.
Day, who was suspended by Labour pending the outcome of the investigation, has been asked to comment.
A Scottish Labour spokesperson said the party took all complaints seriously and that they are investigated in line with party policy.
Day became leader of Edinburgh City Council in 2022.
According to the Sunday Mail, the party's general secretary received a complaint from a constituent in March 2023 alleging Day had sent them "persistent and unsolicited" nude pictures on a dating app.
The complainant said the messages made them feel "deeply uncomfortable".
They told the party's then-general secretary, former MSP James Kelly, that they wanted Labour to speak to Day about his conduct without having to go through a formal process.
The person added: "If that means that the Labour Party will take no action against a perpetrator of sexual harassment, then that's a decision for the Labour Party."
It is understood no formal complaint was made when the allegations were referred to independent investigators.
Anas Sarwar, who has been Scottish Labour leader since 2021, told the Sunday Mail he did not know about the March 2023 complaint.
He said: "We have an independent complaints procedure so if a complaint is made to the Labour Party, the complaint does not come to me and the independent group that looks at complaints does not notify me, as leader, until there is the opening of an investigation.
"As soon as evidence was shared with me - as it was by the Sunday Mail earlier this month - of alleged inappropriate behaviour, then he was suspended the same day."
Day, who remains a councillor but has been replaced as council leader by Labour's Jane Meagher, has since been the subject of fresh accusations.
Two men told The Times they were sent unsolicited messages by Day on a dating app.
He was accused of sending naked pictures of himself, and allegedly became aggressive if ignored.
Scottish Labour said they were not made aware of the claims made in The Times.
City of Edinburgh Council said it dealt with complaints through "established processes" in consultation with an independent whistleblowing service and, where appropriate, Police Scotland.
Police Scotland is investigating a report of inappropriate behaviour made on 22 October.
The force said a previous report had been made about Day earlier this year but no criminality was established in that case.