The Sinn Féin leader is to make a statement in the Dáil (Irish parliament) later regarding an inappropriate text message sent by a former senator to a youth member of the party.
Niall Ó Donnghaile, who was also a former Belfast lord mayor, has said the Police Service of Northern Ireland (PSNI) was notified but no formal complaint was received.
His statement was reported by the Irish News on Tuesday.
BBC News NI has contacted Mr Ó Donnghaile for comment.
It is understood that the text messages were sent by Mr Ó Donnghaile to a 17-year-old in Northern Ireland.
The message is believed to have been personal in nature but not sexually explicit.
The party said when it got the complaint in September 2023, it followed its child protection policy, suspended the person who sent the message, and referred them to police and the social services.
Sinn Féin said the PSNI told it the same month that it was not carrying out an investigation.
Mr Ó Donnghaile later resigned from the party.
On Monday, McDonald said there was no investigation and no charge.
In his statement to the Irish News, Mr Ó Donnghaile said he accepted his behaviour warranted stepping down from his role in the Seanad and as a party member.
He said it would give him “the space to focus on improving” his health and well-being.
He said these are issues he has been dealing with his doctor on since mid-2021.
Time has been set aside for all parties to discuss matters in the Dáil on Tuesday, relating to Sinn Féin’s handling of a separate case involving former press officer Michael McMonagle, who admitted child sex offences.
The party faced criticism after it emerged that two Sinn Féin press officers gave references for their former colleague for a job with a charity.
In September, McMonagle admitted to a series of offences, including attempting to incite a child to engage in sexual activity.
He is due to be sentenced in the coming weeks.
Both press officers, Seán Mag Uidhir and Caolán McGinley, have since resigned.
On this, McDonald said she has instigated an overhaul of procedures in the party.