The NRL has blocked Newcastle hooker Danny Buderus from taking up a coaching role with Super Rugby club the Brumbies.
Earlier on Thursday, the Canberra-based franchise announced the 34-year-old would travel to the nation's capital once a week to assist the Brumbies as their "collision coach".
His new role in teaching tackle-specific skills was described as his preparation for life after league as he enters his final NRL season with the Knights.
But the NRL wasn't willing to authorise the position with its cross-code rivals, given salary cap conditions apply to all currently-contracted players.
"Neither Danny Buderus nor the Knights have sought permission from the NRL to enter into a third party agreement as his playing contract requires and as the club is required under the salary cap rules," NRL interim chief executive Shane Mattiske told Fairfax Media.
"It is hard to envisage any circumstance where an agreement could be approved that allowed a current NRL player to promote another code competing in the same market as an NRL team.
"The announcement today which saw Danny at a press conference in another code's training gear underlines potential issues.
"We will be seeking an immediate response from the Knights and, as much as we respect Danny's intentions, we do not see any way in which the proposal can be pursued."
Buderus earlier described his decision as a golden chance to get a start in the coaching ranks.
But Mattiske said Buderus has access to a range of programs provided by his organisation and the players' association to increase opportunities away from the game.
"In conjunction with the RLPA, we provide a range of specialist services to assist players in maximising off-field careers and these are all available to Danny and all players," said Mattiske.
Buderus has played 242 games for Newcastle and was the last NSW captain to win a State of Origin series - back in 2005.