"The investigators have pointed out the request to interview does not mean those people are under direct suspicion."
Players will be required to co-operate with Asada interviewers under the NRL's code of conduct.
About 10 former players will also be part of the Asada investigation, though the NRL is powerless to punish any players not registered with the code.
Notices will be issued over the next few days, with the interview process to begin on Monday.
The investigation
* 31 players will be issued with a request to be interviewed by Asada.
* Asada informs the NRL if it has an anti-doping case.
* NRL issues infraction notice to any player believed to be guilty of a doping offence.
* Player is stood down by NRL.
* Player attends NRL tribunal, where a decision on guilt and punishment is made.
* Player maintains right to appeal any decision to Wada.
- AAP