The National Rugby League say it may block former Leeds and Australia hooker Danny Buderus' cross-code coaching role with the Brumbies.
The Newcastle Knights player fronted a press conference with Brumbies coach Jake White on Thursday to announce he would be the club's "collision coach" on a one-day-a-week basis next year.
Buderus, who was a member of Leeds' Grand Final-winning team in 2011, plans to play on for Newcastle next season but the NRL is angered it was not consulted by the former New South Wales skipper.
"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 said.
"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 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.
"In conjunction with the RLPA (Rugby League Players' Association) 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."
It is understood Newcastle coach Wayne Bennett gave his permission for the move but the Knights appear to be backtracking.
A statement from the club read: "The final proposed agreement has not yet been seen by the Knights and needs to be submitted to and approved by the NRL to determine if the role can proceed."
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- Danny Buderus
- National Rugby League
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