Rugby Australia's chairperson complained on Friday that the "dark forces" of online criticism had made life miserable for the organisation's first female CEO, who stepped down after a spell of intense pressure.

Paul McLean expressed his "own personal disappointment" at the way Raelene Castle had been treated before she resigned on Thursday, having lost the confidence of the board.

McLean - a former flyhalf who won dozens of caps for the Wallabies - paid tribute to the trailblazing Kiwi, saying a lesser person would have thrown in the towel long ago.

Castle had, he said, been attacked in a "vicious and vitriolic way", particularly on social media, by "silent forces, dark forces".

"She shared some of that with me, which was, you know, I found quite abhorrent."

Castle was the first woman to lead any of Australia's major sports.

Her departure ends a turbulent reign marked by a series of crises and escalating financial problems.

The coronavirus shutdown piled further pressure on the cash-strapped governing body.

McLean said he would adopt the role of executive chairman "for a very short period" while the hunt begins for Castle's replacement.

The ex-Wallaby captain also dismissed a letter from several of his fellow former skippers, calling for change at the top of the organisation.

"Let's be clear here, it's a very small collective of people who've been involved in the game of late," McLean said. "The significance of that group is probably people that aren't on the list."

Two-time World Cup-winner John Eales was among a separate group of ex-captains who criticised the letter, while Michael Lynagh asked to be removed as a signatory.

McLean said that by December this year, two-thirds of Rugby Australia's top positions will have changed in a year.

Rugby Australia laid off most of its staff and slashed players' pay by 60 percent as it grapples with the coronavirus crisis, which looks set to torpedo much of this year's Wallabies schedule.