Gardaí are liaising with French authorities in relation to the alleged rape of an Irish woman in Bordeaux.
According to local media, the 37-year-old woman claimed she was attacked by three men on Sunday night.
Ireland played its opening Rugby World Cup fixture against Romania in the city on Saturday.
The woman was brought to hospital for treatment.
Reports say the alleged attack happened on Rue de la Rousselle, near where the woman was staying.
Gardaí stationed in France for the Rugby World Cup are assisting in the investigation.
In a statement, Gardaí said: "Members of An Garda Síochána currently deployed in France for the duration of the Rugby World Cup tournament to assist Irish people visiting France are liaising with local authorities in relation to an alleged incident.
"The investigation is a matter for French police."
The Irish Rugby Football Union (IRFU) said it was 'shocked' at the news.
"The IRFU is aware of the disturbing news emanating from Bordeaux regarding an incident involving an Irish supporter at the weekend," it said in a statement.
"We are shocked and extend our deepest sympathies to the victim.
"The IRFU wants all fans to have a positive experience supporting the team in France and we urge all travellers to take care and look out for each other," it added.
A spokesperson for the Department of Foreign Affairs has said it was "aware of reports and stands ready to provide consular assistance".