Aileen McColgan has resigned from the investigation due to concerns over its leadership, BBC Newsnight reported.
Her reported departure follows senior counsel Ben Emmerson's resignation a day after he was suspended.
Current chair Professor Alexis Jay, below, became the fourth person to lead the inquiry after Dame Lowell Goddard's resignation.
An inquiry spokeswoman did not confirm or deny Ms McColgan's departure.
She said: "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."
Commons Home Affairs Committee chair Yvette Cooper demanded to know what had "gone wrong" at the inquiry.
A team of senior judges and lawyers are looking into how allegations of sexual abuse were handled by the Anglican and Catholic churches. They will also examine smaller denominations.
Home Secretary Amber Rudd said she still has confidence in the inquiry.
Speaking at a policing conference in London, she said: "I saw the latest news on the inquiry today. I would say it is a matter for the inquiry.
"They are an independent inquiry so they will manage their own recruitment process."
