The Independent Inquiry into Child Abuse has been hit by the resignation of another senior lawyer.
BBC Newsnight understands that Aileen McColgan has quit because of serious concerns over the inquiry's leadership.
She was the barrister leading the inquiry's investigations into the Anglican and Catholic Churches.
The inquiry said that lawyers come and go according to their professional obligations - and a spokeswoman declined to "comment on specifics".
It is understood Aileen McColgan had concerns over the competency of the inquiry's leadership and the way it had previously responded to the resignation of lawyers instructed by it. As well as working on the inquiry, she is also a Professor of Law at King's College London.
It is understood that two other barristers have told the inquiry of their desire to leave because of similar concerns.
The inquiry has suffered a series of setbacks in recent months, including the departures of a number of senior lawyers.
Responding to the latest revelations the Labour MP Lisa Nandy said: "The loss of so many senior members of the inquiry over a short space of time should sound alarm bells for government.
"It really is time that there is some oversight and accountability of this inquiry which is too important to fail."
She added: "We have had a whole series of ministers and civil servants and members of the inquiry panel telling us that the inquiry is back on track and yet repeatedly we learn that there are still issues with the inquiry and it is no wonder that a number of survivors don't have confidence that the inquiry can succeed."
Lawyers who have quit the inquiry:
Hugh Davies QC - deputy counsel to the inquiry (December 2015)
Toby Fisher - joint first junior counsel to the inquiry (August 2015)
Elizabeth Prochaska - joint first junior counsel to the inquiry (September 2016)
Ben Emmerson QC - lead counsel on the inquiry (September 2016)
Aileen McColgan - lead barrister on inquiry investigations into the Anglican and Catholic churches (November 2016)
Yvette Cooper MP, who chairs the Commons Home Affairs Select Committee, said what went wrong must be made clear, adding: "This has got to be about getting it back on track for the survivors of child abuse because they really need to know that this inquiry's going to be effective."
In August the inquiry's third chair Lowell Goddard resigned. She has instructed lawyers to fight newspaper claims that she had made racist remarks.
Then in September the inquiry suspended its most senior lawyer because of concerns over his leadership of the inquiry team. Ben Emmerson resigned from his position 24 hours later.
Last month BBC Newsnight revealed that an investigation into Mr Emmerson's conduct had been dropped despite the inquiry leadership being made aware of an accusation of sexual assault against him - an accusation he strongly denies.
When Mr Emmerson resigned it was agreed that he would continue to work for the inquiry for two months of a handover document. It is thought the inquiry will pay him around £55,000 for his work since resigning.
The inquiry's current chair Professor Alexis Jay is yet to announce a successor to Mr Emmerson. She had faced criticism from survivors' groups because of her background in social work - a profession that they say failed them.
Two weeks ago it emerged that Toby Fisher, one of the first three lawyers on the inquiry, had resigned because he was concerned about the inquiry's "progress and direction".
The inquiry is currently reviewing how it will carry out its investigations.
Aileen McColgan declined to comment.
The Independent Inquiry into Child Sexual Abuse said in a statement: "We have a large legal team comprising a number of junior counsel, senior counsel and solicitors. They come and go subject to their professional obligations and we are not commenting on specifics."