The NRL said it accepted an explanation by Newcastle owner Nathan Tinkler two years ago that he was unaware of rules prohibiting club owners from betting on matches.
The NRL on Wednesday ruled there was no need for further investigation of the incident, which occurred eight days after Tinkler assumed formal ownership of the Knights.
Court documents cited in media reports referred to a bet placed by millionaire mining magnate on August 13, 2011.
Inquiries by the NRL revealed that Tinkler reported the bet to then chief executive David Gallop in 2011 explaining that he had been unaware of the rule preventing an owner from betting.
He also made an undertaking not bet on games in the future.
A check on betting records suggested there was no evidence to indicate any gambling by Tinkler on the Knights since that point.
"It has now transpired that this is a matter that was dealt with by the league at the time," NRL chief operating officer Jim Doyle said.
"It was appropriate that the Integrity Unit look into the issue raised by the reporting of the court material to verify the circumstances, but based on our inquiries no further action is warranted."
