Newcastle superstar Millie Boyle has dropped a bombshell ahead of the Rugby League World Cup, pulling out of the Australian women's team for work reasons.

The NRLW premiership-winning Knights confirmed on Tuesday that Boyle and star fullback Tamika Upton would both miss the Jillaroos' World Cup campaign, with Upton succumbing to a calf injury.

But it is Boyle's decision that could have greater ramifications, after the best front-rower in the women's game informed Jillaroos coach Brad Donald on Tuesday of her decision not to tour to England.

The Knights said Boyle made the call to prioritise her new business working with people living with a disability.

"Millie is all about team-first actions and putting her business and her participants needs ahead of her playing ambitions is the very epitome of team first," Newcastle coach Ronald Griffiths said.

"Such is the nature of the women's game — these are not full-time athletes and as a result decisions are not as straightforward as they may seem.

"There are many factors to consider."

Boyle's call comes as negotiations continue between the NRL and Rugby League Players' Association on a new collective bargaining agreement, with both sides working on a deal for the women's game.

She has long been one of the loudest voices on the need to further professionalise the women's game, as one of the league's best and best-known athletes.

Upton's withdrawal came after she was troubled by a calf injury on the Knights' run to the NRLW premiership.