Pope Francis has said there is not sufficient evidence to open a Church investigation into Canadian cardinal Marc Ouellet over allegations of sexual assault, the Vatican said in a statement.

Cardinal Ouellet, a prominent Vatican official, was named earlier this week in a class action lawsuit against the Quebec Catholic diocese that alleged cases of sexual assault by some 88 priests and staff working there from 1940.

In the filing in Quebec Superior Court, an anonymous complainant alleged that 78-year-old Cardinal Ouellet inappropriately touched her, and made comments that made her feel uncomfortable between 2008 and 2010 when he was archbishop of Quebec.

She was working intern and was 23-years-old at the time, identified only as person "F".

The Vatican was told about the allegations against Cardinal Ouellet in 2021, and Pope Francis appointed a priestly investigator, Jacques Servais, to look into the case.

Mr Servais subsequently advised against launching a full church investigation, the Vatican said.

"Following further relevant consultations, Pope Francis declared that there were not sufficient elements to open a canonical investigation for sexual assault by Cardinal Ouellet against person F," the Vatican statement said.

Cardinal Ouellet heads the Vatican's powerful Congregation for Bishops which advises on which priests should be made bishops.

He is on many experts' short lists of candidates to succeed Pope Francis, after he dies or resigns.

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