Rugby Australia is confident the resignation of chief executive Raelene Castle will not deter Dave Rennie from fulfilling his commitment to coach the Wallabies.

Rennie had given no specific commitment to that end in the wake of Castle's sudden departure on Thursday, but nor had he given any indication his dedication was wavering, a Wallabies source told the Herald.

The New Zealander, who is still contracted to Glasgow in the Pro14, has continued working closely with his Australian-based assistants on building out the Wallabies program.

As speculation intensified around Castle's future, sources close to Rennie had warned twice over the past month that the former Chiefs coach may not be prepared to work under anyone other than the CEO who recruited him.

When Castle handed in her resignation on Thursday evening, one of the first calls both she and director of rugby Scott Johnson made was to Rennie.

A source described the coach's reaction as extremely disappointed but also understanding that best-laid plans can go awry and that he remained committed to coaching Australia.

Incoming Wallabies coach Dave Rennie. AAP

"They had developed a friendship, it was an important relationship to both of them, so there was disappointment on Dave's part," the source said. "But he is also a diligent man who acts with honour. He still wants to do the job."

It would be a major blow to Australian rugby if Rennie were to walk away from his deal, which was due to see him arrive in Australia in late June or early July.

Asked whether Castle’s exit would affect Rennie's arrival, RA chairman Paul McLean said on Friday: “I haven’t spoken to Dave, I spoke to him a couple of weeks ago. [Director of rugby] Scott Johnson spoke to him last night. Raelene has spoken him as well.”

Speaking on ABC’s 7.30 program before standing down on Thursday, Castle said she believed Rennie would honour his commitment.

“I know he has a desperate desire to coach the Wallabies and he has done a lot of work in the time leading up to when he arrives,” Castle said. “He is excited about the young talent he sees coming through on our platforms. That was one of the major reasons he decided to sign with Rugby Australia and come here.

“He will come here regardless of where I sit.”

Even if Rennie does take the job, there is the issue of getting him to Australia due to border restrictions, depending on if and when Tests can be played this year.

Meanwhile, it appears Castle's exit won’t change RA’s support for Gus Pichot at the upcoming World Rugby elections.

McLean made it very clear Australia and other southern hemisphere national unions would not support incumbent chairman Bill Beaumont, who is running against Pichot, the former Argentinian halfback, in next month’s World Rugby Council meetings.

The sticking point is the Nations Championship which never got off the ground. The competition would have pitted southern and northern hemisphere teams against one another but was knocked on the head by a number of Six Nations unions who were concerned about the promotion and relegation aspect and how it could affect their revenues.

It means Beamount, the former England captain, won’t be on Australia’s ticket.

“We were very disappointed that we didn’t get the global competition up and running last year. No greater interest than self interest,” McLean said. “We thought it would have been a defining moment in our game and it was well thought through. We thought it was a no-brainer. That didn’t happen and we made it clear that we were unhappy about that and the process. We stuck together and let it be known to the northern hemisphere. We think it should be revisited sooner rather than later.”